Nonaqueous electrolyte and lithium secondary battery employing the same

ABSTRACT

The invention relates to a nonaqueous electrolyte which comprises a nonaqueous organic solvent and a lithium salt dissolved therein, wherein the nonaqueous organic solvent contains at least one compound selected from the group consisting of acid anhydrides and carbonic esters having an unsaturated bond, and at least one compound selected from the group consisting of sulfonic compounds and fluorine-containing aromatic compounds having 9 carbon atoms or less; and a lithium secondary battery employing the same.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. Ser. No. 10/935,279,filed on Sep. 8, 2004, which is a continuation of PCT/JP03/02741, filedon Mar. 7, 2003, which claims priority to JP 2002-063545, filed on Mar.8, 2002, JP 2002-063547, filed on Mar. 8, 2002, JP 2002-240382, filed onAug. 21, 2002, JP 2002-297359, filed on Oct. 10, 2002, and JP2003-003268, filed on Jan. 9, 2003.

FIELD OF THE INVENTION

The present invention relates to a nonaqueous electrolyte and a lithiumsecondary battery employing the same. More specifically, the inventionrelates to a nonaqueous electrolyte secondary battery of high capacitythat is excellent in discharge characteristics after continuouscharging, storage characteristics, load characteristics, and cyclecharacteristics and that reduces gas generation, and a nonaqueouselectrolyte for use in the battery.

BACKGROUND ART

With the recent trend toward weight reduction and size reduction inelectrical products, development of a lithium secondary battery having ahigh energy density has now been in progress. There is also a desire forimprovements in various battery characteristics as a result of thespread of fields to which lithium secondary batteries are applied.

Moreover, in the case that a lithium secondary battery is used as abackup power source at the time of the power failure or a power sourcefor portable devices, in order to compensate self-discharge, there isusually used a continuous charge method (trickle charge) in which a veryweak current is always applied to maintain the battery in a chargedstate.

A secondary cell using metal lithium as the negative electrode suffersfrom a problem that metallic lithium grows up to form dendrite afterrepeated charging/discharging, and the dendrite reaches the positiveelectrode to thereby cause short-circuit failure inside the cell, whichis a largest obstacle to the practical use of the lithium secondary cellusing metal lithium as the negative electrode. On the contrary, in thecase of a nonaqueous electrolyte secondary battery using as a negativeactive material a carbonaceous material such as coke, artificialgraphite or natural graphite capable of intercalating or releasinglithium, lithium does not grow up to dendrite and hence battery life andsafety can be improved. In particular, a nonaqueous electrolytesecondary battery using a graphite-based carbonaceous material such asartificial graphite or natural graphite attracts attention as a batterycapable of satisfying the requirement of high capacity.

However, in the secondary battery having a negative electrode of agraphite-based carbonaceous material, the electrolyte may decompose onthe surface of the electrode during charging and discharging and thusdecreased efficiency of charging and discharging, decreased cyclecharacteristics, increased inner pressure of the battery caused bygenerated gas, and the like may be sometimes induced.

As a method for obtaining a battery of high capacity, for the purpose ofincreasing the amount of active material of the electrode, it is generalto densify an electrode layer by pressurization in order to reduce thevoids in the electrode layer formed on the current collector of theelectrode as far as possible. However, when the voids in the battery arereduced, the inner pressure of the battery remarkably increases evenwhen the amount of gas generation by the decomposition of theelectrolyte is only a little.

Therefore, with regard to the lithium secondary battery, it is requiredto suppress the decomposition of the electrolyte on the electrodesurface.

In order to suppress the electrolyte of the nonaqueous electrolytesecondary battery using a graphite-based negative electrode, it isproposed to use a nonaqueous solvent containing a cyclic carbonic esterhaving a carbon-carbon unsaturated bond in the molecule, such asvinylene carbonate or a derivative thereof (e.g., see Patent Document1). When the nonaqueous solvent is used, a film formed by reductivedecomposition of the cyclic carbonic ester having an unsaturated bond onthe surface of the negative electrode can suppress excessivedecomposition of the nonaqueous solvent to thereby improve cyclecharacteristics. However, from the experiments of the present inventors,it has been revealed that the secondary battery using a nonaqueoussolvent containing a cyclic carbonic ester having a carbon-carbonunsaturated bond in the molecule has a problem that gas generationincreases when continuous charging is conducted, although it exhibitsexcellent cycle characteristics. It seems that this is because gasgeneration does not decrease because activity of the positive electrodedoes not decrease in the continuous charging in which charging iscontinued at a constant voltage.

In such a situation, there have been reported numerous methods of addingvarious additives for improving initial capacity, rate characteristics,cycle characteristics, high-temperature storage characteristics,low-temperature characteristics, continuous charge characteristics,self-discharge characteristics, overcharge-preventing characteristics,and the like. For example, as methods for improving cyclecharacteristics, there are disclosed the addition of a divalentsulfonate compound such as 1,4-butanediol dimethanesulfonate orpropylene glycol dimethanesulfonate (e.g., see Patent Documents 2 and3), the incorporation of an alkanesulfonic alkyl ester (otherwise, alkylalkanesulfonate) (e.g., see Patent Document 4), and the fact that acycle capacity is increased by incorporating a silyl sulfate such asbis(trialkylsilyl) sulfate (e.g., see Patent Document 5).

Moreover, it is reported that the incorporation of1,4-thioxane-1,1-dioxide in the electrolyte results in the formation ofa complex of cobalt eluted from a positive electrode with1,4-thioxane-1,1-dioxide to stabilize the cobalt ion and to suppress theprecipitation of cobalt on the negative electrode and, as a result, thedecomposition of the electrolyte is suppressed and high-temperaturestorage and high-temperature charge/discharge cycle characteristics areimproved (e.g., see Patent Document 6). In addition, an electrolytecontaining a compound having a molecular weight of less than 500 andhaving an NS structure in which nitrogen and sulfur are bonded is alsoreported (i.e., see Patent Document 7).

Furthermore, in order to improve battery characteristics, safety and thelike, the incorporation of a fluorine-containing aromatic compound inthe nonaqueous solvent is known (i.e., see Patent Documents 8 to 13).However, a method for suppressing gas generation at continuous chargingis not described in any of the literatures.

As a method for improving battery characteristics at continuouscharging, a secondary battery using an electrolyte containing aphosphoric ester is proposed (e.g., see Patent Document 14). However,based on the experiments of the present inventors, the battery isinsufficient in battery characteristics after continuous charging.

[Patent Document 1]

JP-A-8-45545

[Patent Document 2]

JP-A-2000-133304

[Patent Document 3]

JP-A-2001-313071

[Patent Document 4]

JP-A-9-245834

[Patent Document 5]

JP-A-2001-176548

[Patent Document 6]

JP-A-2002-134170

[Patent Document 7]

JP-A-2002-280063

[Patent Document 8]

JP-A-10-112335

[Patent Document 9]

JP-A-11-329496

[Patent Document 10]

JP-A-2000-106209

[Patent Document 11]

JP-A-2001-185213

[Patent Document 12]

JP-A-2001-256996

[Patent Document 13]

JP-A-2002-83629

[Patent Document 14]

JP-A-11-233140

Recently, a higher performance for a lithium secondary battery has beenincreasingly required. That is, it is required to satisfy variouscharacteristics such as high capacity, cycle characteristics,high-temperature storage characteristics, and continuous chargecharacteristics at a high level. In particular, since mobile productsare frequently utilized out of doors and a demand for officenotebook-size personal computers is increasing, the improvement ofcontinuous charge characteristics is particularly much desired in recentyears.

At the time when notebook-size personal computers are used in offices,AC adaptors are used as power sources in most cases and hence thesecondary batteries in the personal computers are continuously charged.In such continuous charging, gas generates owing to the decomposition ofthe electrolyte. In the case of a cylindrical battery in which a safetyvalve is actuated with detecting inner pressure at an abnormal eventsuch as overcharge, the safety valve may be actuated at continuouscharging when a large amount of gas generates.

Moreover, in a prismatic battery without a safety valve, when the amountof gas is large, it becomes necessary to house bare cells in a largercase so that no change is observed in appearance, which leads todecrease in energy density of the whole battery pack. When the gasgeneration is much more, there is a risk of case burst.

Therefore, with regard to the continuous charge characteristics, notonly high recovered capacity and small capacity degradation after testbut also suppression of gas generation during the charging are stronglyrequired. However, the electrolytes hitherto proposed have oftenprovided no improvement of battery characteristics such as thecontinuous charge characteristics.

For example, the use of the electrolyte containing an alkanesulfonicalkyl ester disclosed in the above Patent Document 4 improves capacitydeterioration but the improvement is only a small degree and no effecton the improvement of the continuous charge characteristics isexhibited.

Moreover, since the silyl sulfates disclosed in Patent Document 5 arehighly corrosive and react with cell current collectors, storagecharacteristics, particularly at a high temperature is deteriorated whenthe compounds are incorporated in electrolytes. Furthermore, thetoxicity of the silyl sulfates is unclear in many points but based onthe inference from the fact that dimethyl sulfate, which is an analogouscompound, is regulated by the Ordinance on Prevention of Hazards Due toSpecified Chemical Substances owing to its strong corrosiveness andtoxicity to central nerve system, it may induce a great risk in safetyto incorporate them in electrolytes.

The electrolyte containing 1,4-thioxane-1,1-dioxide (Patent Document 6)improves the capacity deterioration during high-temperature storage butthe improvement is only a small degree and no effect on the improvementof the continuous charge characteristics is exhibited.

Furthermore, 1,1′-sulfonyldiimidazole,N-bismethylthiomethylene-p-toluenesulfonamide, and1-p-tolylsulfonylpyrrole disclosed in Patent Document 7 cannot improveboth of the storage characteristics at a relatively high temperature of80° C. or higher and the continuous charge characteristics.

Accordingly, it is also required to improve the continuous chargecharacteristics in addition to high capacity, high-temperature storagecharacteristics, load characteristics, and cycle characteristics. As thecontinuous charge characteristics, not only reduction of capacitydeterioration but also suppression of gas generation is stronglyrequested.

DISCLOSURE OF THE INVENTION

As a result of the extensive studies for achieving the above objects,the present inventors have found that the above problems can be solvedby incorporating a specific compound in the electrolyte, and thus theinvention has been accomplished.

Namely, the gist of the invention lies in a nonaqueous electrolytecomprising a nonaqueous organic solvent and a lithium salt dissolvedtherein, wherein the nonaqueous organic solvent comprises at least onecompound selected from the group consisting of acid anhydrides andcarbonic esters having an unsaturated bond, and at least one compoundselected from the group consisting of [A] and [B], or in a lithiumsecondary battery employing the same.

-   [A]: Sulfonic compounds represented by any one of the following    formulae (1) to (5):    wherein L¹ represents a Z¹-valent connecting group composed of    carbon atom(s) and hydrogen atoms, R¹ represents a hydrocarbon    group, and Z¹ is an integer of 3 or more;    wherein L² represents a Z²-valent connecting group composed of    carbon atom(s) and hydrogen atoms, R² represents a fluorinated    aliphatic saturated hydrocarbon group, n² is an integer of 1 or    more, and Z² is an integer of 2 or more;    wherein each of R³ to R⁷ independently represents a hydrogen atom or    a hydrocarbon group having 1 to 8 carbon atoms, R⁸ represents a    hydrocarbon group having 1 to 8 carbon atoms, and n³ represents an    integer of 0 to 4;    wherein each of R⁹ to R¹² independently represents a hydrogen atom    or a hydrocarbon group having 1 to 8 carbon atoms, or R⁹ and R¹⁰,    R¹¹ and R¹² each may be combined with each other to form a ring and    R¹⁰ and R¹¹ may be also combined with each other; and    wherein each of R¹³ to R¹⁵ independently represents an alkyl group    having 1 to 12 carbon atoms which may be substituted with fluorine    atom(s), an alkenyl group having 2 to 12 carbon atoms which may be    substituted with fluorine atom(s), an aryl group having 6 to 12    carbon atoms which may be substituted with fluorine atom(s), or an    aralkyl group having 7 to 12 carbon atoms which may be substituted    with fluorine atom(s), or R¹⁴ and R¹⁵ may be combined with each    other to form a nitrogen-containing aliphatic ring and R¹³ and R¹⁴    may be combined with each other to form a cyclic structure;-   [B]: fluorine-containing aromatic compounds having 9 carbon atoms or    less.

The use of the electrolyte comprising at least one compound selectedfrom the group consisting of acid anhydrides and carbonic esters havingan unsaturated bond, and at least one compound selected from the groupconsisting of the above [A] and [B] improves high-temperature storagecharacteristics and continuous charge characteristics with maintainingexcellent cycle characteristics and high capacity. Specifically,self-discharge hardly occurs during the exposure to a high temperature,the recovered capacity after the exposure is improved, and also therecovered capacity after continuous charging for a long period can beremarkably improved.

The detail of the reason why the electrolyte according to the inventionprovides the improvement of high-temperature storage characteristics andcontinuous charge characteristics is unclear but the fact that a surfaceprotecting film (hereinafter sometimes referred to as “SEI”) formed onthe negative electrode at the initial stage of charging is thermallystable is considered to contribute. When the SEI inhibiting the reactionbetween lithium and the electrolyte at the negative electrode isthermally unstable, the reaction between lithium and the electrolyteproceeds to cause capacity deterioration. A nonaqueous solventrepresented by a saturated carbonic ester is reduced at the initialstage of charging to form SEI and, at that time, at least one compoundselected from the group consisting of [A] and [B] is in part reduced andincorporated into SEI. It is presumed that SEI becomes stronger by thepresence of reduced products of both of at least one compound selectedfrom the group consisting of [A] and [B] and the compound selected fromacid anhydrides and carbonic esters having an unsaturated bond.

Moreover, when at least one compound selected from the above [A] isadded, it is considered that the remaining compound not reduced at theinitial stage of charging acts as an acid to cover the basic point ofthe positive active material and thereby the reaction between thepositive active material and the electrolyte, which generates gases suchas carbon dioxide, is inhibited.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view illustrating the structure ofa sheet-form lithium secondary battery obtained by carrying out theinvention.

With regard to the symbols in the drawing, 1 is a positive electrode, 2is a negative electrode, 3 is a separator, 4 is a PET film, 5 is asilicone rubber, 6 is a glass plate, 7 is a laminate film, and 8 is alead with a sealant.

BEST MODE FOR CARRYING OUT THE INVENTION

The following will describe modes for carrying out the invention indetail.

The nonaqueous electrolyte according to the invention comprises anonaqueous organic solvent and a lithium salt dissolved therein, andfurther contains at least one compound selected from among [A] and [B].

[A] Sulfonic Compounds:

Sulfonic compounds of [A] group are selected from the following formulae(1) to (5):

wherein L¹ represents a Z¹-valent connecting group composed of carbonatom(s) and hydrogen atoms, R¹ represents a hydrocarbon group, and Z¹ isan integer of 3 or more;

wherein L² represents a Z²-valent connecting group composed of carbonatom(s) and hydrogen atoms, R² represents a fluorinated aliphaticsaturated hydrocarbon group, n² is an integer of 1 or more, and Z² is aninteger of 2 or more;

wherein each of R³ to R⁷ independently represents a hydrogen atom or ahydrocarbon group having 1 to 8 carbon atoms, R⁸ represents ahydrocarbon group having 1 to 8 carbon atoms, and n³ represents aninteger of 0 to 4;

wherein each of R⁹ to R¹² independently represents a hydrogen atom or ahydrocarbon group having 1 to 8 carbon atoms, or R⁹ and R¹⁰, R¹¹ and R¹²each may be combined with each other to form a ring and R¹⁰ and R¹¹ maybe also combined with each other; and

wherein each of R¹³ to R¹⁵ independently represents an alkyl grouphaving 1 to 12 carbon atoms which may be substituted with fluorineatom(s), an alkenyl group having 2 to 12 carbon atoms which may besubstituted with fluorine atom(s), an aryl group having 6 to 12 carbonatoms which may be substituted with fluorine atom(s), or an aralkylgroup having 7 to 12 carbon atoms which may be substituted with fluorineatom(s), or R¹⁴ and R¹⁵ may be combined with each other to form anitrogen-containing aliphatic ring and R¹³ and R¹⁴ may be combined witheach other to form a cyclic structure.

In the above formula (1), R¹ represents a hydrocarbon group. Examples ofthe hydrocarbon group include alkyl groups having 1 to 4 carbon atoms,such as a methyl group, an ethyl group, a propyl group, an isopropylgroup, and a butyl group; alkenyl groups having 2 to 4 carbon atoms,such as a vinyl group, an isopropenyl group, and an allyl group; arylgroups having 6 to 9 carbon atoms, such as a phenyl group, a tolylgroup, an ethylphenyl group, a dimethylphenyl group, and trimethylphenylgroup; aralkyl groups having 7 to 8 carbon atoms, such as benzyl groupand a phenethyl group. Preferred are alkyl groups having 1 to 2 carbonatoms, such as a methyl group and an ethyl group, and aryl groups having6 to 9 carbon atoms, such as a phenyl group, a tolyl group, anethylphenyl group, a dimethylphenyl group, and trimethylphenyl group,and more preferred are a methyl group and a tolyl group.

Moreover, the above Z¹ represents an integer of 3 or more, and ispreferably 3 or 4. Furthermore, L¹ represents a Z¹-valent connectinggroup composed of carbon atom(s) and hydrogen atoms. The number of thecarbon atoms constituting the connecting group L¹ is preferably 3 to 12,more preferably 3 to 8.

When the above Z¹ is 3, L¹ represents a trivalent connecting groupcomposed of carbon atoms and hydrogen atoms. The following willexemplify the group.

Moreover, when the above Z¹ is 4, L¹ represents a tetravalent connectinggroup composed of carbon atoms and hydrogen atoms. The following willexemplify the group.

Examples of the multivalent sulfonate compound represented by the aboveformula (1) include trivalent sulfonates, e.g., 1,2,3-propanetrioltrisulfonates such as 1,2,3-propanetriol trimethanesulfonate,1,2,3-propanetriol triethanesulfonate, 1,2,3-propanetrioltripropanesulfonate, 1,2,3-propanetriol tributanesulfonate,1,2,3-propanetriol tribenzenesulfonate, 1,2,3-propanetrioltri-p-toluenesulfonate, 1,2,3-propanetriol tri-4-ethylbenzenesulfonate,1,2,3-propanetriol tris-3,5-dimethylbenzenesulfonate, and1,2,3-propanetriol tri-2-mesitylenesulfonate, 1,2,3-butanetrioltrisulfonates such as 1,2,3-butanetriol trimethanesulfonate,1,2,3-butanetriol triethanesulfonate, 1,2,3-butanetrioltripropanesulfonate, 1,2,3-butanetriol tributanesulfonate,1,2,3-butanetriol tribenzenesulfonate, 1,2,3-butanetrioltri-p-toluenesulfonate, 1,2,3-butanetriol tri-4-ethylbenzenesulfonate,1,2,3-butanetriol tris-3,5-dimethylbenzenesulfonate, and1,2,3-butanetriol tri-2-mesitylenesulfonate, 1,2,4-butanetrioltrisulfonates such as 1,2,4-butanetriol trimethanesulfonate,1,2,4-butanetriol triethanesulfonate, 1,2,4-butanetrioltripropanesulfonate, 1,2,4-butanetriol tributanesulfonate,1,2,4-butanetriol tribenzenesulfonate, 1,2,4-butanetrioltri-p-toluenesulfonate, 1,2,4-butanetriol tri-4-ethylbenzenesulfonate,1,2,4-butanetriol tris-3,5-dimethylbenzenesulfonate, and1,2,4-butanetriol tri-2-mesitylenesulfonate, 1,2,5-pentanetrioltrisulfonates such as 1,2,5-pentanetriol trimethanesulfonate,1,2,5-pentanetriol triethanesulfonate, 1,2,5-pentanetrioltripropanesulfonate, 1,2,5-pentanetriol tribenzenesulfonate, and1,2,5-pentanetriol tri-p-toluenesulfonate, 1,2,6-hexanetrioltrisulfonates such as 1,2,6-hexanetriol trimethanesulfonate,1,2,6-hexanetriol triethanesulfonate, 1,2,6-hexanetrioltripropanesulfonate, 1,2,6-hexanetriol tribenzenesulfonate, and1,2,6-hexanetriol tri-p-toluenesulfonate, 1,2,3-heptanetrioltrisulfonates such as 1,2,3-heptanetriol trimethanesulfonate,1,2,3-heptanetriol triethanesulfonate, 1,2,3-heptanetrioltripropanesulfonate, 1,2,3-heptanetriol tribenzenesulfonate, and1,2,3-heptanetriol tri-p-toluenesulfonate, 1,2,7-heptanetrioltrisulfonates such as 1,2,7-heptanetriol trimethanesulfonate,1,2,7-heptanetriol triethanesulfonate, 1,2,7-heptanetrioltripropanesulfonate, 1,2,7-heptanetriol tribenzenesulfonate, and1,2,7-heptanetriol tri-p-toluenesulfonate, 1,2,8-octanetrioltrisulfonates such as 1,2,8-octanetriol trimethanesulfonate,1,2,8-octanetriol triethanesulfonate, 1,2,8-octanetrioltripropanesulfonate, 1,2,8-octanetriol tribenzenesulfonate, and1,2,8-octanetriol tri-p-toluenesulfonate, trimethylolethanetrisulfonates such as trimethylolethane trimethanesulfonate,trimethylolethane triethanesulfonate, trimethylolethanetripropanesulfonate, trimethylolethane tributanesulfonate,trimethylolethane tribenzenesulfonate, trimethylolethanetri-p-toluenesulfonate, trimethylolethane tri-4-ethylbenzenesulfonate,trimethylolethane tris-3,5-dimethylbenzenesulfonate, andtrimethylolethane tri-2-mesitylenesulfonate, trimethylolpropanetrisulfonates such as trimethylolpropane trimethanesulfonate,trimethylolpropane triethanesulfonate, trimethylolpropanetripropanesulfonate, trimethylolpropane tributanesulfonate,trimethylolpropane tribenzenesulfonate, trimethylolpropanetri-p-toluenesulfonate, trimethylolpropane tri-4-ethylbenzenesulfonate,trimethylolpropane tris-3,5-dimethylbenzenesulfonate, andtrimethylolpropane tri-2-mesitylenesulfonate,3-methylpentane-1,3,5-triol trisulfonates such as3-methylpentane-1,3,5-triol trimethanesulfonate,3-methylpentane-1,3,5-triol triethanesulfonate,3-methylpentane-1,3,5-triol tripropanesulfonate,3-methylpentane-1,3,5-triol tributanesulfonate,3-methylpentane-1,3,5-triol tribenzenesulfonate,3-methylpentane-1,3,5-triol tri-p-toluenesulfonate,3-methylpentane-1,3,5-triol tri-4-ethylbenzenesulfonate,3-methylpentane-1,3,5-triol tris-3,5-dimethylbenzenesulfonate, and3-methylpentane-1,3,5-triol tri-2-mesitylenesulfonate,1,2,4-benzenetriol trisulfonates such as 1,2,4-benzenetrioltrimethanesulfonate, 1,2,4-benzenetriol triethanesulfonate,1,2,4-benzenetriol tripropanesulfonate, 1,2,4-benzenetrioltribenzenesulfonate, and 1,2,4-benzenetriol tri-p-toluenesulfonate, andthe like; and tetravalent sulfonates, e.g., 1,2,3,4-butanetetraoltetrasulfonates such as 1,2,3,4-butanetetraol tetramethanesulfonate,1,2,3,4-butanetetraol tetraethanesulfonate, 1,2,3,4-butanetetraoltetrapropanesulfonate, 1,2,3,4-butanetetraol tetrabenzenesulfonate,1,2,3,4-butanetetraol tetra-p-toluenesulfonate, 1,2,3,4-butanetetraoltetra-4-ethylbenzenesulfonate, and 1,2,3,4-butanetetraoltetrakis-3,5-dimethylbenzenesulfonate; pentaerythritol tetrasulfonatessuch as pentaerythritol tetramethanesulfonate, pentaerythritoltetraethanesulfonate, pentaerythritol tetrapropanesulfonate,pentaerythritol tetrabenzenesulfonate, pentaerythritoltetra-p-toluenesulfonate, pentaerythritol tetra-4-ethylbenzenesulfonate,and pentaerythritol tetrakis-3,5-dimethylbenzenesulfonate, and the like.

Preferred are trivalent sulfonates, e.g., 1,2,3-propanetrioltrisulfonates such as 1,2,3-propanetriol trimethanesulfonate,1,2,3-propanetriol triethanesulfonate, 1,2,3-propanetrioltribenzenesulfonate, and 1,2,3-propanetriol tri-p-toluenesulfonate,1,2,3-butanetriol trisulfonates such as 1,2,3-butanetrioltrimethanesulfonate, 1,2,3-butanetriol triethanesulfonate,1,2,3-butanetriol tribenzenesulfonate, and 1,2,3-butanetrioltri-p-toluenesulfonate, 1,2,4-butanetriol trisulfonates such as1,2,4-butanetriol trimethanesulfonate, 1,2,4-butanetrioltriethanesulfonate, 1,2,4-butanetriol tribenzenesulfonate, and1,2,4-butanetriol tri-p-toluenesulfonate, trimethylolpropanetrisulfonates such as trimethylolpropane trimethanesulfonate,trimethylolpropane triethanesulfonate, trimethylolpropanetribenzenesulfonate, and trimethylolpropane tri-p-toluenesulfonate,3-methylpentane-1,3,5-triol trisulfonates such as3-methylpentane-1,3,5-triol trimethanesulfonate,3-methylpentane-1,3,5-triol triethanesulfonate,3-methylpentane-1,3,5-triol tribenzenesulfonate, and3-methylpentane-1,3,5-triol tri-p-toluenesulfonate, and the like; andtetravalent sulfonates, e.g., 1,2,3,4-butanetetraol tetrasulfonates suchas 1,2,3,4-butanetetraol tetramethanesulfonate, 1,2,3,4-butanetetraoltetraethanesulfonate, 1,2,3,4-butanetetraol tetrabenzenesulfonate,1,2,3,4-butanetetraol tetra-p-toluenesulfonate, pentaerythritoltetrasulfonates such as pentaerythritol tetramethanesulfonate,pentaerythritol tetraethanesulfonate, pentaerythritoltetrabenzenesulfonate, and pentaerythritol tetra-p-toluenesulfonate, andthe like.

More preferred are trivalent methanesulfonates and p-toluenesulfonates,such as 1,2,3-propanetriol trimethanesulfonate, 1,2,3-propanetrioltri-p-toluenesulfonate, 1,2,3-butanetriol trimethanesulfonate,1,2,3-butanetriol tribenzenesulfonate, 1,2,3-butanetrioltri-p-toluenesulfonate, 1,2,4-butanetriol trimethanesulfonate,1,2,4-butanetriol tri-p-toluenesulfonate, trimethylolpropanetrimethanesulfonate, trimethylolpropane tri-p-toluenesulfonate,3-methylpentane-1,3,5-triol trimethanesulfonate, and3-methylpentane-1,3,5-triol tri-p-toluenesulfonate.

In the above formula (2), R² represents a fluorinated aliphaticsaturated hydrocarbon group. With regard to the degree offluorine-substitution in the aliphatic saturated hydrocarbon group,substitution of a part of hydrogen atoms thereof with fluorine atom(s)may be sufficient but all the hydrogen atoms may be substituted withfluorine atoms.

Examples thereof include linear perfluoroalkyl groups such as atrifluoromethyl group, a pentafluoroethyl group, a heptafluoropropylgroup, a perfluorobutyl group, a perfluoropentyl group, a perfluorohexylgroup, a perfluoroheptyl group, a perfluorooctyl group, and aperfluorodecyl group, branched perfluoroalkyl groups such as aperfluoro-1-methylethyl group, a perfluoro-3-methylbutyl group, aperfluoro-5-methylhexyl group, and a perfluoro-7-methyloctyl group,partially fluorinated linear alkyl groups such as a fluoromethyl group,a difluoromethyl group, a 1,1,2,2-tetrafluoroethyl group, a1,1,1,2-tetrafluoroethyl group, a 1,1,2,2,3,3,4,4-octafluorobutyl group,and a 1,1,2,2,3,3,4,4,5,5,6,6-dodecafluorohexyl group, partiallyfluorinated branched alkyl groups such as 1,1,1,2,3,3-hexafluoropropylgroup and 1,1-bis(trifluoromethyl)ethyl group, and the like.

Moreover, the above n² represents an integer of 1 or more, and ispreferably an integer of 1 to 6, more preferably 1 or 2.

Furthermore, the above Z² represents an integer of 2 or more, and ispreferably an integer of 2 to 4. Additionally, L² represents a Z²-valentconnecting group composed of carbon atom(s) and hydrogen atoms. Thenumber of the carbon atoms constituting the connecting group L² ispreferably 3 to 12, more preferably 3 to 8.

When the above Z² is 2, L² represents a divalent connecting groupcomposed of carbon atoms and hydrogen atoms. The following willexemplify the group.

Moreover, when Z² is 3, L² represents a trivalent connecting groupcomposed of carbon atoms and hydrogen atoms. The following willexemplify the group.

Furthermore, when the above Z² is 4, L² represents a tetravalentconnecting group composed of carbon atoms and hydrogen atoms. Thefollowing will exemplify the group.

Examples of the fluorine-containing sulfonate compound represented bythe formula (2) include divalent sulfonates, e.g., ethanedioldisulfonates such as ethanediol bis(2,2,2-trifluoroethanesulfonate),ethanediol bis(2,2,3,3,3-pentafluoropropanesulfonate), ethanediolbis(2,2,3,3,4,4,4-heptafluorobutanesulfonate), ethanediolbis(2,2,3,3-tetrafluoropropanesulfonate), ethanediolbis(2,2,3,3,4,4-hexafluorobutanesulfonate), ethanediolbis(2,2,3,3,4,4,5,5-octafluoropentanesulfonate), ethanediolbis(2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptanesulfonate), ethanediolbis(2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9-hexadecafluoroheptanesulfonate),ethanediol bis(2,2,3,4,4,4-hexafluorobutanesulfonate), ethanediolbis(3,3,4,4,4-pentafluorobutanesulfonate), ethanediolbis(3,3,4,4,5,5,6,6,6-nonafluorohexanesulfonate), ethanediolbis(3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctanesulfonate), ethanediolbis(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecanesulfonate),ethanediol bis{2-(perfluoro-3-methylbutyl)ethanesulfonate}, ethanediolbis{2-(perfluoro-5-methylhexyl)ethanesulfonate}, ethanediolbis{2-(perfluoro-5-methyloctyl)ethanesulfonate}, ethanediolbis{2-(perfluoro-5-methyloctyl)ethanesulfonate}, ethanediolbis(4,4,5,5,6,6,7,7,7-nonafluoroheptanesulfonate), and ethanediolbis(7,7,8,8,9,9,10,10,10-nonafluorodecanesulfonate), 1,2-propanedioldisulfonates such as 1,2-propanediolbis(2,2,2-trifluoroethanesulfonate), 1,2-propanediolbis(2,2,3,3,3-pentafluoropropanesulfonate), 1,2-propanediolbis(2,2,3,3,4,4,4-heptafluorobutanesulfonate), 1,2-propanediolbis(2,2,3,3-tetrafluoropropanesulfonate), 1,2-propanediolbis(2,2,3,3,4,4-hexafluorobutanesulfonate), 1,2-propanediolbis(2,2,3,3,4,4,5,5-octafluoropentanesulfonate), 1,2-propanediolbis(2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptanesulfonate),1,2-propanediolbis(2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9-hexadecafluoroheptanesulfonate),1,2-propanediol bis(2,2,3,4,4,4-hexafluorobutanesulfonate),1,2-propanediol bis(3,3,4,4,4-pentafluorobutanesulfonate),1,2-propanediol bis(3,3,4,4,5,5,6,6,6-nonafluorohexanesulfonate),1,2-propanediolbis(3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctanesulfonate),1,2-propanediolbis(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecanesulfonate),1,2-propanediol bis{2-(perfluoro-3-methylbutyl)ethanesulfonate},1,2-propanediol bis{2-(perfluoro-5-methylhexyl)ethanesulfonate},1,2-propanediol bis{2-(perfluoro-5-methyloctyl)ethanesulfonate},1,2-propanediol bis{2-(perfluoro-5-methyloctyl)ethanesulfonate},1,2-propanediol bis(4,4,5,5,6,6,7,7,7-nonafluoroheptanesulfonate), and1,2-propanediol bis(7,7,8,8,9,9,10,10,10-nonafluorodecanesulfonate),1,3-propanediol disulfonate such as 1,3-propanediolbis(2,2,2-trifluoroethanesulfonate), 1,3-propanediolbis(2,2,3,3,3-pentafluoropropanesulfonate), 1,3-propanediolbis(2,2,3,3,4,4,4-heptafluorobutanesulfonate), 1,3-propanediolbis(2,2,3,3-tetrafluoropropanesulfonate), 1,3-propanediolbis(2,2,3,3,4,4-hexafluorobutanesulfonate), 1,3-propanediolbis(2,2,3,3,4,4,5,5-octafluoropentanesulfonate), 1,3-propanediolbis(2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptanesulfonate),1,3-propanediolbis(2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9-hexadecafluoroheptanesulfonate),1,3-propanediol bis(2,2,3,4,4,4-hexafluorobutanesulfonate),1,3-propanediol bis(3,3,4,4,4-pentafluorobutanesulfonate),1,3-propanediol bis(3,3,4,4,5,5,6,6,6-nonafluorohexanesulfonate),1,3-propanediolbis(3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctanesulfonate),1,3-propanediolbis(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecanesulfonate),1,3-propanediol bis{2-(perfluoro-3-methylbutyl)ethanesulfonate},1,3-propanediol bis{2-(perfluoro-5-methylhexyl)ethanesulfonate},1,3-propanediol bis{2-(perfluoro-5-methyloctyl)ethanesulfonate},1,3-propanediol bis{2-(perfluoro-5-methyloctyl)ethanesulfonate},1,3-propanediol bis(4,4,5,5,6,6,7,7,7-nonafluoroheptanesulfonate), and1,3-propanediol bis(7,7,8,8,9,9,10,10,10-nonafluorodecanesulfonate),1,2-butanediol disulfonate such as 1,2-butanediolbis(2,2,2-trifluoroethanesulfonate), 1,2-butanediolbis(2,2,3,3,3-pentafluoropropanesulfonate), 1,2-butanediolbis(2,2,3,3,4,4,4-heptafluorobutanesulfonate), 1,2-butanediolbis(3,3,4,4,5,5,6,6,6-nonafluorohexanesulfonate), and 1,2-butanediolbis(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecanesulfonate),1,3-butanediol disulfonate such as 1,3-butanediolbis(2,2,2-trifluoroethanesulfonate), 1,3-butanediolbis(2,2,3,3,3-pentafluoropropanesulfonate), 1,3-butanediolbis(2,2,3,3,4,4,4-heptafluorobutanesulfonate), 1,3-butanediolbis(3,3,4,4,5,5,6,6,6-nonafluorohexanesulfonate), and 1,3-butanediolbis(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecanesulfonate),1,4-butanediol disulfonate such as 1,4-butanediolbis(2,2,2-trifluoroethanesulfonate), 1,4-butanediolbis(2,2,3,3,3-pentafluoropropanesulfonate), 1,4-butanediolbis(2,2,3,3,4,4,4-heptafluorobutanesulfonate), 1,4-butanediolbis(2,2,3,3-tetrafluoropropanesulfonate), 1,4-butanediolbis(2,2,3,3,4,4-hexafluorobutanesulfonate), 1,4-butanediolbis(2,2,3,3,4,4,5,5-octafluoropentanesulfonate), 1,4-butanediolbis(2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptanesulfonate),1,4-butanediolbis(2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9-hexadecafluoroheptanesulfonate),1,4-butanediol bis(2,2,3,4,4,4-hexafluorobutanesulfonate),1,4-butanediol bis(3,3,4,4,4-pentafluorobutanesulfonate), 1,4-butanediolbis(3,3,4,4,5,5,6,6,6-nonafluorohexanesulfonate), 1,4-butanediolbis(3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctanesulfonate),1,4-butanediolbis(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecanesulfonate),1,4-butanediol bis{2-(perfluoro-3-methylbutyl)ethanesulfonate},1,4-butanediol bis{2-(perfluoro-5-methylhexyl)ethanesulfonate},1,4-butanediol bis{2-(perfluoro-5-methyloctyl)ethanesulfonate},1,4-butanediol bis{2-(perfluoro-5-methyloctyl)ethanesulfonate},1,4-butanediol bis(4,4,5,5,6,6,7,7,7-nonafluoroheptanesulfonate), and1,4-butanediol bis(7,7,8,8,9,9,10,10,10-nonafluorodecanesulfonate),1,4-benzenediol disulfonate such as 1,4-benzenediolbis(2,2,2-trifluoroethanesulfonate), 1,4-benzenediolbis(2,2,3,3,3-pentafluoropropanesulfonate), 1,4-benzenediolbis(2,2,3,3,4,4,4-heptafluorobutanesulfonate), 1,4-benzenediolbis(3,3,4,4,5,5,6,6,6-nonafluorohexanesulfonate), and 1,4-benzenediolbis(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecanesulfonate),and the like; trivalent sulfonates, e.g., 1,2,3-propanetrioltrisulfonate such as 1,2,3-propanetrioltris(2,2,2-trifluoroethanesulfonate), 1,2,3-propanetrioltris(2,2,3,3,3-pentafluoropropanesulfonate), 1,2,3-propanetrioltris(2,2,3,3,4,4,4-heptafluorobutanesulfonate), 1,2,3-propanetrioltris(3,3,4,4,5,5,6,6,6-nonafluorohexanesulfonate), and1,2,3-propanetrioltris(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecanesulfonate),1,2,3-butanetriol trisulfonate such as 1,2,3-butanetrioltris(2,2,2-trifluoroethanesulfonate), 1,2,3-butanetrioltris(2,2,3,3,3-pentafluoropropanesulfonate), 1,2,3-butanetrioltris(2,2,3,3,4,4,4-heptafluorobutanesulfonate), 1,2,3-butanetrioltris(3,3,4,4,5,5,6,6,6-nonafluorohexanesulfonate), and 1,2,3-butanetrioltris(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecanesulfonate),1,2,4-butanetriol trisulfonate such as 1,2,4-butanetrioltris(2,2,2-trifluoroethanesulfonate), 1,2,4-butanetrioltris(2,2,3,3,3-pentafluoropropanesulfonate), 1,2,4-butanetrioltris(2,2,3,3,4,4,4-heptafluorobutanesulfonate), 1,2,4-butanetrioltris(3,3,4,4,5,5,6,6,6-nonafluorohexanesulfonate), and 1,2,4-butanetrioltris(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecanesulfonate),trimethylolethane trisulfonate such as trimethylolethanetris(2,2,2-trifluoroethanesulfonate), trimethylolethanetris(2,2,3,3,3-pentafluoropropanesulfonate), trimethylolethanetris(2,2,3,3,4,4,4-heptafluorobutanesulfonate), trimethylolethanetris(3,3,4,4,5,5,6,6,6-nonafluorohexanesulfonate), and trimethylolethanetris(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecanesulfonate),trimethylolpropane trisulfonate such as trimethylolpropanetris(2,2,2-trifluoroethanesulfonate), trimethylolpropanetris(2,2,3,3,3-pentafluoropropanesulfonate), trimethylolpropanetris(2,2,3,3,4,4,4-heptafluorobutanesulfonate), trimethylolpropanetris(3,3,4,4,5,5,6,6,6-nonafluorohexanesulfonate), andtrimethylolpropanetris(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecanesulfonate),3-methylpentane-1,3,5-triol trisulfonate such as3-methylpentane-1,3,5-triol tris(2,2,2-trifluoroethanesulfonate),3-methylpentane-1,3,5-triol tris(2,2,3,3,3-pentafluoropropanesulfonate),3-methylpentane-1,3,5-trioltris(2,2,3,3,4,4,4-heptafluorobutanesulfonate),3-methylpentane-1,3,5-trioltris(3,3,4,4,5,5,6,6,6-nonafluorohexanesulfonate), and3-methylpentane-1,3,5-trioltris(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecanesulfonate),1,2,4-benzenetriol trisulfonate such as 1,2,4-benzenetrioltris(2,2,2-trifluoroethanesulfonate), 1,2,4-benzenetrioltris(2,2,3,3,3-pentafluoropropanesulfonate), 1,2,4-benzenetrioltris(2,2,3,3,4,4,4-heptafluorobutanesulfonate), 1,2,4-benzenetrioltris(3,3,4,4,5,5,6,6,6-nonafluorohexanesulfonate), and1,2,4-benzenetrioltris(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecanesulfonate),and the like; and tetravalent sulfonates, e.g., 1,2,3,4-butanetetraoltetrasulfonate such as 1,2,3,4-butanetetraoltetrakis(2,2,2-trifluoroethanesulfonate), 1,2,3,4-butanetetraoltetrakis(2,2,3,3,3-pentafluoropropanesulfonate), 1,2,3,4-butanetetraoltetrakis(2,2,3,3,4,4,4-heptafluorobutanesulfonate),1,2,3,4-butanetetraoltetrakis(3,3,4,4,5,5,6,6,6-nonafluorohexanesulfonate), and1,2,3,4-butanetetraoltetrakis(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecanesulfonate),pentaerythritol tetrasulfonate such as pentaerythritoltetrakis(2,2,2-trifluoroethanesulfonate), pentaerythritoltetrakis(2,2,3,3,3-pentafluoropropanesulfonate), pentaerythritoltetrakis(2,2,3,3,4,4,4-heptafluorobutanesulfonate), pentaerythritoltetrakis(3,3,4,4,5,5,6,6,6-nonafluorohexanesulfonate), andpentaerythritoltetrakis(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecanesulfonate),and the like.

Preferred are divalent perfluoroalkylmethanesulfonates such asethanediol bis(2,2,2-trifluoroethanesulfonate), ethanediolbis(2,2,3,3,3-pentafluoropropanesulfonate), ethanediolbis(2,2,3,3,4,4,4-heptafluorobutanesulfonate), 1,2-propanediolbis(2,2,2-trifluoroethanesulfonate), 1,2-propanediolbis(2,2,3,3,3-pentafluoropropanesulfonate), 1,2-propanediolbis(2,2,3,3,4,4,4-heptafluorobutanesulfonate), 1,3-propanediolbis(2,2,2-trifluoroethanesulfonate), 1,3-propanediolbis(2,2,3,3,3-pentafluoropropanesulfonate), 1,3-propanediolbis(2,2,3,3,4,4,4-heptafluorobutanesulfonate), 1,2-butanediolbis(2,2,2-trifluoroethanesulfonate), 1,2-butanediolbis(2,2,3,3,3-pentafluoropropanesulfonate), 1,2-butanediolbis(2,2,3,3,4,4,4-heptafluorobutanesulfonate), 1,3-butanediolbis(2,2,2-trifluoroethanesulfonate), 1,3-butanediolbis(2,2,3,3,3-pentafluoropropanesulfonate), 1,3-butanediolbis(2,2,3,3,4,4,4-heptafluorobutanesulfonate), 1,4-butanediolbis(2,2,2-trifluoroethanesulfonate), 1,4-butanediolbis(2,2,3,3,3-pentafluoropropanesulfonate), 1,4-butanediolbis(2,2,3,3,4,4,4-heptafluorobutanesulfonate), and the like; trivalentperfluoroalkylmethanesulfonates such as 1,2,3-propanetrioltris(2,2,2-trifluoroethanesulfonate), 1,2,3-propanetrioltris(2,2,3,3,3-pentafluoropropanesulfonate), 1,2,3-butanetrioltris(2,2,2-trifluoroethanesulfonate), 1,2,3-butanetrioltris(2,2,3,3,3-pentafluoropropanesulfonate), 1,2,4-butanetrioltris(2,2,2-trifluoroethanesulfonate), 1,2,4-butanetrioltris(2,2,3,3,3-pentafluoropropanesulfonate), trimethylolethanetris(2,2,2-trifluoroethanesulfonate), trimethylolethanetris(2,2,3,3,3-pentafluoropropanesulfonate), trimethylolpropanetris(2,2,2-trifluoroethanesulfonate), trimethylolpropanetris(2,2,3,3,3-pentafluoropropanesulfonate), 3-methylpentane-1,3,5-trioltris(2,2,2-trifluoroethanesulfonate), 3-methylpentane-1,3,5-trioltris(2,2,3,3,3-pentafluoropropanesulfonate), and the like; andtetravalent perfluoroalkylmethanesulfonates such as1,2,3,4-butanetetraol tetrakis(2,2,2-trifluoroethanesulfonate),1,2,3,4-butanetetraol tetrakis(2,2,3,3,3-pentafluoropropanesulfonate),pentaerythritol tetrakis(2,2,2-trifluoroethanesulfonate),pentaerythritol tetrakis(2,2,3,3,3-pentafluoropropanesulfonate), and thelike.

In the above formula (3), each of R³ to R⁵ independently represents ahydrogen atom or a hydrocarbon group having 1 to 8 carbon atoms.Examples of the hydrocarbon group include alkyl groups having 1 to 8carbon atoms, such as a methyl group, an ethyl group, a propyl group, anisopropyl group, and a butyl group; alkenyl groups having 2 to 8 carbonatoms, such as a vinyl group, an isopropenyl group, and an allyl group;aryl groups having 6 to 8 carbon atoms, such as a phenyl group, a tolylgroup, an ethylphenyl group, and a dimethylphenyl group; aralkyl groupshaving 7 to 8 carbon atoms, such as a benzyl group and a phenethylgroup. Of these, preferred are alkyl groups having 1 to 4 carbon atomsand alkenyl groups having 2 to 4 carbon atoms, and more preferred arealkyl groups having 1 to 4 carbon atoms.

R⁶ and R⁷ each independently represents a hydrogen atom or a hydrocarbongroup having 1 to 8 carbon atoms. Examples of the hydrocarbon groupinclude alkyl groups having 1 to 8 carbon atoms, such as a methyl group,an ethyl group, a propyl group, an isopropyl group, and a butyl group;alkenyl groups having 2 to 8 carbon atoms, such as a vinyl group, anisopropenyl group, and an allyl group; aryl groups having 6 to 8 carbonatoms, such as a phenyl group, a tolyl group, an ethylphenyl group, anda dimethylphenyl group; aralkyl groups having 7 to 8 carbon atoms, suchas a benzyl group and a phenethyl group. Of these, preferred is ahydrogen atom, an alkyl group having 1 to 3 carbon atoms, an alkenylgroup having 2 to 4 carbon atoms, a phenyl group, a tolyl group, abenzyl group, or a phenethyl group, and more preferred is a hydrogenatom or a methyl group.

R⁸ represents a hydrocarbon group having 1 to 8 carbon atoms. Examplesof the hydrocarbon group include alkyl groups having 1 to 8 carbonatoms, such as a methyl group, an ethyl group, a propyl group, anisopropyl group, and a butyl group; alkenyl groups having 2 to 8 carbonatoms, such as a vinyl group, an isopropenyl group, and an allyl group;aryl groups having 6 to 8 carbon atoms, such as a phenyl group, a tolylgroup, an ethylphenyl group, and a dimethylphenyl group; aralkyl groupshaving 7 to 8 carbon atoms, such as a benzyl group and a phenethylgroup. Of these, preferred is an alkyl group having 1 to 4 carbon atoms,an alkenyl group having 2 to 4 carbon atoms, a phenyl group or a tolylgroup, and more preferred is a methyl group, an ethyl group, a phenylgroup, or a tolyl group.

n³ represents an integer of 0 to 4, preferably an integer of 0 to 2,more preferably 0.

Specific examples of the compound represented by the formula (3) includethe following.

(i) Silyl(alkyl) methanesulfonates: There are mentioned trimethylsilylmethanesulfonate, triethylsilyl methanesulfonate, tripropylsilylmethanesulfonate, triisopropylsilyl methanesulfonate, tributylsilylmethanesulfonate, triisobutylsilyl methanesulfonate, tri-t-butylsilylmethanesulfonate, trihexylsilyl methanesulfonate, triphenylsilylmethanesulfonate, tribenzylsilyl methanesulfonate, ethyldimethylsilylmethanesulfonate, dimethylpropylsilyl methanesulfonate,dimethylisopropylsilyl methanesulfonate, butyldimethylsilylmethanesulfonate, t-butyldimethylsilyl methanesulfonate,dimethyloctylsilyl methanesulfonate, diethylisopropylsilylmethanesulfonate, octyldiisopropylsilyl methanesulfonate,dimethylphenylsilyl methanesulfonate, dimethylphenethylsilylmethanesulfonate, benzyldimethylsilyl methanesulfonate,vinyldimethylsilyl methanesulfonate, allyldimethylsilylmethanesulfonate, trimethylsilylmethyl methanesulfonate,1-(trimethylsilyl)ethyl methanesulfonate, 2-(trimethylsilyl)ethylmethanesulfonate, 3-(trimethylsilyl)propyl methanesulfonate, and thelike.

Of these, preferred are trialkylsilyl methanesulfonates wherein all ofR³ to R⁵ are alkyl groups having 1 to 4 carbon atoms and n³ is 0, suchas trimethylsilyl methanesulfonate, triethylsilyl methanesulfonate,tripropylsilyl methanesulfonate, triisopropylsilyl methanesulfonate,tributylsilyl methanesulfonate, triisobutylsilyl methanesulfonate,tri-t-butylsilyl methanesulfonate, ethyldimethylsilyl methanesulfonate,dimethylpropylsilyl methanesulfonate, dimethylisopropylsilylmethanesulfonate, butyldimethylsilyl methanesulfonate,t-butyldimethylsilyl methanesulfonate, and diethylisopropylsilylmethanesulfonate.

(ii) Silyl(alkyl) ethanesulfonates: There are mentioned trimethylsilylethanesulfonate, triethylsilyl ethanesulfonate, tripropylsilylethanesulfonate, triisopropylsilyl ethanesulfonate, tributylsilylethanesulfonate, triisobutylsilyl ethanesulfonate, tri-t-butylsilylethanesulfonate, trihexylsilyl ethanesulfonate, triphenylsilylethanesulfonate, tribenzylsilyl ethanesulfonate, ethyldimethylsilylethanesulfonate, dimethylpropylsilyl ethanesulfonate,dimethylisopropylsilyl ethanesulfonate, butyldimethylsilylethanesulfonate, t-butyldimethylsilyl ethanesulfonate,dimethyloctylsilyl ethanesulfonate, diethylisopropylsilylethanesulfonate, octyldiisopropylsilyl ethanesulfonate,dimethylphenylsilyl ethanesulfonate, dimethylphenethylsilylethanesulfonate, benzyldimethylsilyl ethanesulfonate, vinyldimethylsilylethanesulfonate, allyldimethylsilyl ethanesulfonate,trimethylsilylmethyl ethanesulfonate, 1-(trimethylsilyl)ethylethanesulfonate, 2-(trimethylsilyl)ethyl ethanesulfonate,3-(trimethylsilyl)propyl ethanesulfonate, and the like.

Of these, preferred are trialkylsilyl ethanesulfonates wherein all of R³to R⁵ are alkyl groups having 1 to 4 carbon atoms and n3 is 0, such astrimethylsilyl ethanesulfonate, triethylsilyl ethanesulfonate,tripropylsilyl ethanesulfonate, triisopropylsilyl ethanesulfonate,tributylsilyl ethanesulfonate, triisobutylsilyl ethanesulfonate,tri-t-butylsilyl ethanesulfonate, ethyldimethylsilyl ethanesulfonate,dimethylpropylsilyl ethanesulfonate, dimethylisopropylsilylethanesulfonate, butyldimethylsilyl ethanesulfonate,t-butyldimethylsilyl ethanesulfonate, and diethylisopropylsilylethanesulfonate.

(iii) Silyl(alkyl) propanesulfonates: There are mentioned trimethylsilylpropanesulfonate, triethylsilyl propanesulfonate, tripropylsilylpropanesulfonate, triisopropylsilyl propanesulfonate, tributylsilylpropanesulfonate, triisobutylsilyl propanesulfonate, tri-t-butylsilylpropanesulfonate, trihexylsilyl propanesulfonate, triphenylsilylpropanesulfonate, tribenzylsilyl propanesulfonate, ethyldimethylsilylpropanesulfonate, dimethylpropylsilyl propanesulfonate,dimethylisopropylsilyl propanesulfonate, butyldimethylsilylpropanesulfonate, t-butyldimethylsilyl propanesulfonate,dimethyloctylsilyl propanesulfonate, diethylisopropylsilylpropanesulfonate, octyldiisopropylsilyl propanesulfonate,dimethylphenylsilyl propanesulfonate, dimethylphenethylsilylpropanesulfonate, benzyldimethylsilyl propanesulfonate,vinyldimethylsilyl propanesulfonate, allyldimethylsilylpropanesulfonate, trimethylsilylmethyl propanesulfonate,1-(trimethylsilyl)ethyl propanesulfonate, 2-(trimethylsilyl)ethylpropanesulfonate, 3-(trimethylsilyl)propyl propanesulfonate, and thelike. (iv) Silyl(alkyl) butanesulfonates: There are mentionedtrimethylsilyl butanesulfonate, triethylsilyl butanesulfonate,tripropylsilyl butanesulfonate, triisopropylsilyl butanesulfonate,tributylsilyl butanesulfonate, triisobutylsilyl butanesulfonate,tri-t-butylsilyl butanesulfonate, trihexylsilyl butanesulfonate,triphenylsilyl butanesulfonate, tribenzylsilyl butanesulfonate,ethyldimethylsilyl butanesulfonate, dimethylpropylsilyl butanesulfonate,dimethylisopropylsilyl butanesulfonate, butyldimethylsilylbutanesulfonate, t-butyldimethylsilyl butanesulfonate,dimethyloctylsilyl butanesulfonate, diethylisopropylsilylbutanesulfonate, octyldiisopropylsilyl butanesulfonate,dimethylphenylsilyl butanesulfonate, dimethylphenethylsilylbutanesulfonate, benzyldimethylsilyl butanesulfonate, vinyldimethylsilylbutanesulfonate, allyldimethylsilyl butanesulfonate,trimethylsilylmethyl butanesulfonate, 1-(trimethylsilyl)ethylbutanesulfonate, 2-(trimethylsilyl)ethyl butanesulfonate,3-(trimethylsilyl)propyl butanesulfonate, and the like.

(v) Silyl(alkyl) benzenesulfonates: There are mentioned trimethylsilylbenzenesulfonate, triethylsilyl benzenesulfonate, tripropylsilylbenzenesulfonate, triisopropylsilyl benzenesulfonate, tributylsilylbenzenesulfonate, triisobutylsilyl benzenesulfonate, tri-t-butylsilylbenzenesulfonate, trihexylsilyl benzenesulfonate, triphenylsilylbenzenesulfonate, tribenzylsilyl benzenesulfonate, ethyldimethylsilylbenzenesulfonate, dimethylpropylsilyl benzenesulfonate,dimethylisopropylsilyl benzenesulfonate, butyldimethylsilylbenzenesulfonate, t-butyldimethylsilyl benzenesulfonate,dimethyloctylsilyl benzenesulfonate, diethylisopropylsilylbenzenesulfonate, octyldiisopropylsilyl benzenesulfonate,dimethylphenylsilyl benzenesulfonate, dimethylphenethylsilylbenzenesulfonate, benzyldimethylsilyl benzenesulfonate,vinyldimethylsilyl benzenesulfonate, allyldimethylsilylbenzenesulfonate, trimethylsilylmethyl benzenesulfonate,1-(trimethylsilyl)ethyl benzenesulfonate, 2-(trimethylsilyl)ethylbenzenesulfonate, 3-(trimethylsilyl)propyl benzenesulfonate, and thelike.

Of these, preferred are trialkylsilyl benzenesulfonates wherein all ofR³ to R⁵ are alkyl groups having 1 to 4 carbon atoms and n³ is 0, suchas trimethylsilyl benzenesulfonate, triethylsilyl benzenesulfonate,tripropylsilyl benzenesulfonate, triisopropylsilyl benzenesulfonate,tributylsilyl benzenesulfonate, triisobutylsilyl benzenesulfonate,tri-t-butylsilyl benzenesulfonate, ethyldimethylsilyl benzenesulfonate,dimethylpropylsilyl benzenesulfonate, dimethylisopropylsilylbenzenesulfonate, butyldimethylsilyl benzenesulfonate,t-butyldimethylsilyl benzenesulfonate, and diethylisopropylsilylbenzenesulfonate.

(vi) Silyl(alkyl)-p-toluenesulfonates: There are mentionedtrimethylsilyl-p-toluenesulfonate, triethylsilyl-p-toluenesulfonate,tripropylsilyl-p-toluenesulfonate, triisopropylsilyl-p-toluenesulfonate,tributylsilyl-p-toluenesulfonate, triisobutylsilyl-p-toluenesulfonate,tri-t-butylsilyl-p-toluenesulfonate, trihexylsilyl-p-toluenesulfonate,triphenylsilyl-p-toluenesulfonate, tribenzylsilyl-p-toluenesulfonate,ethyldimethylsilyl-p-toluenesulfonate,dimethylpropylsilyl-p-toluenesulfonate,dimethylisopropylsilyl-p-toluenesulfonate,butyldimethylsilyl-p-toluenesulfonate,t-butyldimethylsilyl-p-toluenesulfonate,dimethyloctylsilyl-p-toluenesulfonate,diethylisopropylsilyl-p-toluenesulfonate,octyldiisopropylsilyl-p-toluenesulfonate,dimethylphenylsilyl-p-toluenesulfonate,dimethylphenethylsilyl-p-toluenesulfonate,benzyldimethylsilyl-p-toluenesulfonate,vinyldimethylsilyl-p-toluenesulfonate,allyldimethylsilyl-p-toluenesulfonate,trimethylsilylmethyl-p-toluenesulfonate,1-(trimethylsilyl)ethyl-p-toluenesulfonate,2-(trimethylsilyl)ethyl-p-toluenesulfonate,3-(trimethylsilyl)propyl-p-toluenesulfonate, and the like.

Of these, preferred are trialkylsilyl-p-toluenesulfonates wherein R³ toR⁵ are alkyl groups having 1 to 4 carbon atoms and n³ is 0, such astrimethylsilyl-p-toluenesulfonate, triethylsilyl-p-toluenesulfonate,tripropylsilyl-p-toluenesulfonate, triisopropylsilyl-p-toluenesulfonate,tributylsilyl-p-toluenesulfonate, triisobutylsilyl-p-toluenesulfonate,tri-t-butylsilyl-p-toluenesulfonate,ethyldimethylsilyl-p-toluenesulfonate,dimethylpropylsilyl-p-toluenesulfonate,dimethylisopropylsilyl-p-toluenesulfonate,butyldimethylsilyl-p-toluenesulfonate,t-butyldimethylsilyl-p-toluenesulfonate, anddiethylisopropylsilyl-p-toluenesulfonate.

(vii) Silyl(alkyl)-4-ethylbenzenesulfonates: There are mentionedtrimethylsilyl-4-ethylbenzenesulfonate,triethylsilyl-4-ethylbenzenesulfonate,tripropylsilyl-4-ethylbenzenesulfonate,triisopropylsilyl-4-ethylbenzenesulfonate,tributylsilyl-4-ethylbenzenesulfonate,triisobutylsilyl-4-ethylbenzenesulfonate,tri-t-butylsilyl-4-ethylbenzenesulfonate,trihexylsilyl-4-ethylbenzenesulfonate,triphenylsilyl-4-ethylbenzenesulfonate,tribenzylsilyl-4-ethylbenzenesulfonate,ethyldimethylsilyl-4-ethylbenzenesulfonate,dimethylpropylsilyl-4-ethylbenzenesulfonate,dimethylisopropylsilyl-4-ethylbenzenesulfonate,butyldimethylsilyl-4-ethylbenzenesulfonate,t-butyldimethylsilyl-4-ethylbenzenesulfonate,dimethyloctylsilyl-4-ethylbenzenesulfonate,diethylisopropylsilyl-4-ethylbenzenesulfonate,octyldiisopropylsilyl-4-ethylbenzenesulfonate,dimethylphenylsilyl-4-ethylbenzenesulfonate,dimethylphenethylsilyl-4-ethylbenzenesulfonate,benzyldimethylsilyl-4-ethylbenzenesulfonate,vinyldimethylsilyl-4-ethylbenzenesulfonate,allyldimethylsilyl-4-ethylbenzenesulfonate,trimethylsilylmethyl-4-ethylbenzenesulfonate,1-(trimethylsilyl)ethyl-4-ethylbenzenesulfonate,2-(trimethylsilyl)ethyl-4-ethylbenzenesulfonate,3-(trimethylsilyl)propyl-4-ethylbenzenesulfonate, and the like.

(viii) Silyl-3,5-dimethylbenzenesulfonates: There are mentionedtrimethylsilyl-3,5-dimethylbenzenesulfonate,triethylsilyl-3,5-dimethylbenzenesulfonate,tripropylsilyl-3,5-dimethylbenzenesulfonate,triisopropylsilyl-3,5-dimethylbenzenesulfonate,tributylsilyl-3,5-dimethylbenzenesulfonate,triisobutylsilyl-3,5-dimethylbenzenesulfonate,tri-t-butylsilyl-3,5-dimethylbenzenesulfonate,trihexylsilyl-3,5-dimethylbenzenesulfonate,triphenylsilyl-3,5-dimethylbenzenesulfonate,tribenzylsilyl-3,5-dimethylbenzenesulfonate,ethyldimethylsilyl-3,5-dimethylbenzenesulfonate,dimethylpropylsilyl-3,5-dimethylbenzenesulfonate,dimethylisopropylsilyl-3,5-dimethylbenzenesulfonate,butyldimethylsilyl-3,5-dimethylbenzenesulfonate,t-butyldimethylsilyl-3,5-dimethylbenzenesulfonate,dimethyloctylsilyl-3,5-dimethylbenzenesulfonate,diethylisopropylsilyl-3,5-dimethylbenzenesulfonate,octyldiisopropylsilyl-3,5-dimethylbenzenesulfonate,dimethylphenylsilyl-3,5-dimethylbenzenesulfonate,dimethylphenethylsilyl-3,5-dimethylbenzenesulfonate,benzyldimethylsilyl-3,5-dimethylbenzenesulfonate,vinyldimethylsilyl-3,5-dimethylbenzenesulfonate,allyldimethylsilyl-3,5-dimethylbenzenesulfonate,trimethylsilyl-3,5-dimethylbenzenesulfonate,1-(trimethylsilyl)ethyl-3,5-dimethylbenzenesulfonate,2-(trimethylsilyl)ethyl-3,5-dimethylbenzenesulfonate,3-(trimethylsilyl)propyl-3,5-dimethylbenzenesulfonate, and the like.

In this connection, the molecular weight of the compound represented bythe formula (3) is usually 400 or less, preferably 300 or less. When themolecular weight is too large, there is a possibility that an effect ofimprovement of the continuous charge characteristics according to theinvention cannot satisfactory be exhibited owing to poor solubility tothe electrolyte.

In the above formula (4), each of R⁹ to R¹² independently represents ahydrogen atom or a hydrocarbon group having 1 to 8 carbon atoms.Examples of the hydrocarbon group include alkyl groups having 1 to 8carbon atoms, such as a methyl group, an ethyl group, a propyl group, anisopropyl group, and a butyl group; alkenyl groups having 2 to 8 carbonatoms, such as a vinyl group, an isopropenyl group, and an allyl group;aryl groups having 6 to 8 carbon atoms, such as a phenyl group, a tolylgroup, an ethylphenyl group, and a dimethylphenyl group; aralkyl groupshaving 7 to 8 carbon atoms, such as a benzyl group and a phenethylgroup. Of these, preferred is a hydrogen atom, an alkyl group having 1to 4 carbon atoms or an alkenyl group having 2 to 4 carbon atoms, andmore preferred is a methyl group or an ethyl group.

In the case that R⁹ and R¹⁰ or R¹¹ and R¹² are combined with each otherto form a ring, an aliphatic hydrocarbon ring having 3 to 8, preferably5 to 6 carbon atoms inclusive of the carbon atom to which R⁹ and R¹⁰ orR¹¹ and R¹² are attached. In the case that R¹⁰ and R¹¹ are combined witheach other, examples of the bond include a single bond, —CH₂—, —CH₂CH₂—,and the like, and preferred is a single bond.

The following are mentioned as specific examples of the compoundrepresented by the formula (4). Of these, preferred are1,4-thioxane-1,1-dioxide derivatives.

(ix) 1,4-Thioxane-1,1-dioxide derivatives: There are mentioned1,4-thioxane-1,1-dioxide (R⁹ to R¹²=H),3-methyl-1,4-thioxane-1,1-dioxide (R⁹=methyl group, R¹⁰ to R¹²=H),3-ethyl-1,4-thioxane-1,1-dioxide (R⁹=ethyl group, R¹⁰ to R¹²=H),3-propyl-1,4-thioxane-1,1-dioxide (R⁹=propyl group, R¹⁰ to R¹²=H),3-butyl-1,4-thioxane-1,1-dioxide (R⁹=butyl group, R¹⁰ to R¹²=H),3,5-dimethyl-1,4-thioxane-1,1-dioxide (R⁹ and R¹¹=methyl group, R¹⁰ andR¹²=H), 3,5-diethyl-1,4-thioxane-1,1-dioxide (R⁹ and R¹¹=ethyl group,R¹⁰ and R^( =H),) 3-ethyl-5-methyl-1,4-thioxane-1,1-dioxide (R⁹=ethylgroup, R¹¹=methyl group, R¹⁰ and R¹²=H),3-phenyl-1,4-thioxane-1,1-dioxide (R⁹=phenyl group, R¹⁰ to R¹²=H),3-vinyl-1,4-thioxane-1,1-dioxide (R⁹=vinyl group, R¹⁰ to R¹²=H),3-allyl-1,4-thioxane-1,1-dioxide (R⁹=allyl group, R¹⁰ to R¹²=H),3-benzyl-1,4-thioxane-1,1-dioxide (R⁹=benzyl group, R¹⁰ to R¹²=H), andthe like.

Of these, preferred are 1,4-thioxane-1,1-dioxide derivatives whereineach of R⁹ to R¹² is a hydrogen atom, a methyl group, or an ethyl group,such as 1,4-thioxane-1,1-dioxide, 3-methyl-1,4-thioxane-1,1-dioxide,3-ethyl-1,4-thioxane-1,1-dioxide, and3,5-dimethyl-1,4-thioxane-1,1-dioxide. Particularly preferred are1,4-thioxane-1,1-dioxide and 3-methyl-1,4-thioxane-1,1-dioxide.

(x) 3,4-Epoxytetrahydrothiophene-1,1-dioxide derivatives: There arementioned 3,4-epoxytetrahydrothiophene-1,1-dioxide (R¹⁰ and R¹¹ form asingle bond, R⁹ and R¹²=H),1-methyl-6-oxa-3-thia-bicyclo(3.1.0)hexane-3,3-dioxide (R¹⁰ and R¹¹ forma single bond, R⁹=methyl group, R¹²=H),1-ethyl-6-oxa-3-thia-bicyclo(3.1.0)hexane-3,3-dioxide (R¹⁰ and R¹¹ forma single bond, R⁹=ethyl group, R¹²=H),1-propyl-6-oxa-3-thia-bicyclo(3.1.0)hexane-3,3-dioxide (R¹⁰ and R¹¹ forma single bond, R⁹=propyl group, R¹²=H),1-butyl-6-oxa-3-thia-bicyclo(3.1.0)hexane-3,3-dioxide (R¹⁰ and R¹¹ forma single bond, R⁹=butyl group, R¹²=H),1,5-dimethyl-6-oxa-3-thia-bicyclo(3.1.0)hexane-3,3-dioxide (R¹⁰ and R¹¹form a single bond, R⁹ and R¹²=methyl group),1,5-diethyl-6-oxa-3-thia-bicyclo(3.1.0)hexane-3,3-dioxide (R¹⁰ and R¹¹form a single bond, R⁹ and R¹²=ethyl group), and the like.

Of these, preferred are 3,4-epoxytetrahydrothiophene-1,1-dioxideswherein the tetrahydrothiophene may be substituted with a methyl groupeach at the 3- and 4-positions, such as3,4-epoxytetrahydrothiophene-1,1-dioxide,1-methyl-6-oxa-3-thia-bicyclo(3.1.0)hexane-3,3-dioxide, and1,5-dimethyl-6-oxa-3-thia-bicyclo(3.1.0)hexane-3,3-dioxide.Particularly, preferred is 3,4-epoxytetrahydrothiophene-1,1-dioxide.

In this connection, the molecular weight of the compound represented bythe formula (4) is usually 250 or less, preferably 180 or less. When themolecular weight is too large, there is a possibility that the effectsof improvement of the high-temperature storage characteristics and thecontinuous charge characteristics according to the invention cannotsatisfactory be exhibited owing to poor solubility to the electrolyte.

In the above formula (5), each of R¹³ to R¹⁵ independently represents analkyl group having 1 to 12 carbon atoms which may be substituted withfluorine atom(s), an alkenyl group having 2 to 12 carbon atoms which maybe substituted with fluorine atom(s), an aryl group having 6 to 12carbon atoms which may be substituted with fluorine atom(s) or anaralkyl group having 7 to 12 carbon atoms which may be substituted withfluorine atom(s).

Examples of the alkyl group having 1 to 12 carbon atoms include a methylgroup, an ethyl group, an n-propyl group, an i-propyl group, an n-butylgroup, an i-butyl group, a sec-butyl group, a tert-butyl group, a pentylgroup, and the like. Of theses, preferred are alkyl groups having 1 to 8carbon atoms, particularly alkyl groups having 1 to 4 carbon atoms.

Examples of the alkenyl groups having 2 to 12 carbon atoms include avinyl group, a propenyl group, and the like. Preferred are those having2 to 8 carbon atoms, particularly those having 2 to 4 carbon atoms.

Examples of the aryl group having 6 to 12 carbon atoms include a phenylgroup, a tolyl group, a xylyl group, and the like. Of these, preferredis a phenyl group.

Examples of the aralkyl group having 7 to 12 carbon atom include abenzyl group, a phenethyl group, and the like.

In these alkyl group, alkenyl group, aryl group, and aralkyl group, apart of or all of hydrogen atoms may be substituted with fluorine atomsbut preferred are those which are not substituted with any fluorineatom.

R¹⁴ and R¹⁵ may be combined with each other to form anitrogen-containing aliphatic ring and, as the nitrogen-containingaliphatic ring, pyrrolidine, piperidine, and the like are mentioned.

R¹³ and R¹⁴ may be combined with each other to form a cyclic structureand, as the cyclic structure, sultams are mentioned.

Specific examples of the compound represented by the formula (5) includemethanesulfonamides such as N,N-dimethylmethanesulfonamide,N,N-diethylmethanesulfonamide, N,N-dipropylmethanesulfonamide,N-methyl-N-ethylmethanesulfonamide, N-methyl-N-benzylmethanesulfonamide,1-methanesulfonylpyrrolidine, 1-methanesulfonylpiperidine, andN,N-bistrifluoromethylmethanesulfonamide; ethanesulfonamides such asN,N-diethylethanesulfonamide, N,N-dimethylethanesulfonamide, andN-methyl-N-ethylethanesulfonamide; vinylsulfonamides such asN,N-dimethylvinylsulfonamide; benzenesulfonamides such asN,N-dimethylbenzenesulfonamide, N,N-diethylbenzenesulfonamide,N,N-dipropylbenzenesulfonamide, and N,N-dibutylbenzenesulfonamide;trifluoromethanesulfonamides such asN,N-dimethyltrifluoromethanesulfonamide andN,N-bistrifluoromethyltrifluoromethanesulfonamide;pentafluoroethanesulfonamides such asN,N-dimethylpentafluoroethanesulfonamide; sultams such asN-methylpropanesultam, N-ethylpropanesultam, N-butylpropanesultam,N-methylbutanesultam, N-ethylbutanesultam, N-propylbutanesultam; and thelike.

Of these, preferred are methanesulfonamides and ethanesulfonamides.Because of little gas generation and high residual capacity afterhigh-temperature storage, particularly preferred areN,N-dimethylmethanesulfonamide, N,N-diethylmethanesulfonamide,N,N-diethylethanesulfonamide, and N,N-dimethylethanesulfonamide.

[B]: Fluorine-Containing Aromatic Compounds having 9 Carbon Atoms orLess:

Examples of the fluorine-containing aromatic compounds having 9 carbonatoms or less include fluorobenzene, 1,2-difluorobenzene,1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-trifluorobenzene,1,2,4-trifluorobenzene, 1,3,5-trifluorobenzene,1,2,3,4-tetrafluorobenzene, 1,2,3,5-tetrafluorobenzene,1,2,4,5-tetrafluorobenzene, pentafluorobenzene, hexafluorobenzene,2-fluorotoluene, 3-fluorotoluene, 4-fluorotoluene, 2,3-difluorotoluene,2,4-difluorotoluene, 2,5-difluorotoluene, 2,6-difluorotoluene,3,4-difluorotoluene, benzotrifluoride, 2-fluorobenzotrifluoride,3-fluorobenzotrifluoride, 4-fluorobenzotrifluoride, 3-fluoro-o-xylene,4-fluoro-o-xylene, 2-fluoro-m-xylene, 5-fluoro-m-xylene,2-methylbenzotrifluoride, 3-methylbenzotrifluoride,4-methylbenzotrifluoride, octafluorotoluene, and the like. Of these,preferred are fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene,1,4-difluorobenzene, 2-fluorotoluene, and 3-fluorotoluene, andparticularly preferred is fluorobenzene.

The fluorine-containing aromatic compound having 10 carbon atoms or moreis not preferred because the load characteristics are decreased.

At least one compound selected from the group consisting of the above[A] and [B] (hereinafter sometimes abbreviated as “additive”) may beused singly or as a mixture of two or more thereof. At that time, thecompounds selected from the same compound group or different compoundgroups can be used in combination.

The adding amount of the additive is not particularly limited but thetotal amount may be usually 0.01% by weight or more based on thenonaqueous electrolyte. When the amount is smaller that the value,high-temperature storage characteristics, continuous chargecharacteristics, and the like cannot be improved. The additive isincorporated so that the amount becomes preferably 0.05% by weight ormore, more preferably 0.1% by weight or more, particularly preferably0.3% by weight or more.

To the contrary, when the ratio of the additive in the nonaqueouselectrolyte is too large, the ion conductivity is lowered and hencebattery characteristics such as rate characteristics are deteriorated.Therefore, although the upper limit depends on the chemical species ofthe additive, the limit is usually 15% by weight or less, preferably 10%by weight or less, more preferably 7% by weight or less, particularlypreferably 5% by weight or less. Furthermore, in the case of using atleast one compound selected from the group consisting of [A] as theadditive, the amount is further preferably 3% by weight or less.

In this connection, in the case of using a compound represented by theformula (1) or (2) of [A] as the additive, the total content of theadditive is preferably 0.01 to 15% by weight, more preferably 0.1 to 7%by weight, most preferably 3% by weight or less based on the nonaqueouselectrolyte. In the case of using a compound represented by the formula(3) of [A], the total content of the additive is more preferably 0.01 to15% by weight, most preferably 3% by weight or less based the nonaqueouselectrolyte. In the case of using a compound represented by the formula(4) of [A], the total content of the additive is more preferably 0.01 to10% by weight, most preferably 0.1 to 2.5% by weight or less based onthe nonaqueous electrolyte.

In the case of using a compound represented by the formula (5) of [A],the total content of the additive is more preferably 0.01 to 5% byweight based on the nonaqueous electrolyte. Moreover, in the case ofusing a compound of [B] as the additive, the total content of theadditive is more preferably 0.01 to 10% by weight based on thenonaqueous electrolyte.

The nonaqueous electrolyte according to the present invention comprises,in addition to the above additives, at least one compound selected fromthe group consisting of acid anhydrides and carbonic esters having anunsaturated bond in the nonaqueous organic solvent.

Examples of the acid anhydride include carboxylic anhydrides such assuccinic anhydride, glutaric anhydride, maleic anhydride, citraconicanhydride, glutaconic anhydride, itaconic anhydride, diglycolicanhydride, cyclohexanedicarboxylic anhydride,cyclopentanetetracarboxylic dianhydride, and phenylsuccinic anhydride.

The carbonic ester having an unsaturated bond is not particularlylimited as far as it has a carbon-carbon double bond or a carbon-carbontriple bond in the molecule and may be either of linear one or cyclicone.

Example of the carbonic ester having an unsaturated bond includevinylene carbonate compounds such as vinylene carbonate, methylvinylenecarbonate, ethylvinylene carbonate, 4,5-dimethylvinylene carbonate,4,5-diethylvinylene carbonate, fluorovinylene carbonate,trifluoromethylvinylene carbonate, phenylvinylene carbonate, and4,5-diphenylvinylene carbonate; vinylethylene carbonate compounds suchas vinylethylene carbonate, 4-methyl-4-vinylethylene carbonate,4-ethyl-4-vinylethylene carbonate, 4-n-propyl-4-vinylethylene carbonate,5-methyl-4-vinylethylene carbonate, 4,4-divinylethylene carbonate,4,5-divinylethylene carbonate, phenylethylene carbonate, and4,5-diphenylethylene carbonate; methyleneethylene carbonate compoundssuch as 4,4-dimethyl-5-methyleneethylene carbonate and4,4-diethyl-5-methyleneethylene carbonate; phenyl carbonate compoundssuch as diphenyl carbonate, methyl phenyl carbonate, and t-butyl phenylcarbonate; vinyl carbonate compounds such as divinyl carbonate andmethyl vinyl carbonate; allyl carbonate compounds such as diallylcarbonate and allyl methyl carbonate; and the like.

Of these, preferred are unsaturated cyclic carbonic esters such asvinylene carbonate compounds and ethylene carbonate compoundssubstituted with an aromatic ring or a substituent having acarbon-carbon unsaturated bond. In particular, preferred is vinylenecarbonate, 4,5-dimethylvinylene carbonate, 4,5-diphenylvinylenecarbonate, vinylethylene carbonate, 4-methyl-4-vinylethylene carbonate,or 4,5-divinylethylene carbonate, and particularly preferred is vinylenecarbonate or vinylethylene carbonate.

These compounds may be used singly or in combination of two or morethereof. At that time, the compounds selected from the same compoundgroup or different compound groups can be used in combination.

The cycle characteristics of the cell can be improved by incorporatinginto the electrolyte at least one compound selected from the groupconsisting of acid anhydrides and carbonic esters having an unsaturatedbond in the molecule. The reason is not clear but is presumed that astable protective film can be formed on the surface of the negativeelectrode. When the content is small, the characteristics are notsufficiently improved.

In this connection, there is a problem that the incorporation of atleast one compound selected from the group consisting of acid anhydridesand carbonic esters having an unsaturated bond in the electrolytegenerally increases gas generation, but the combined use of theaforementioned additive compound can suppress the increase of gasgeneration. However, when the content is too large, gas generates duringthe storage at a high temperature to increase the inner pressure of thebattery in some cases, so that the content is preferably within thefollowing range.

The ratio of at least one compound selected from the group consisting ofacid anhydrides and carbonic esters having an unsaturated bond in themolecule in the nonaqueous electrolyte is usually 0.01% by weight ormore, preferably 0.05% by weight or more, particularly preferably 0.1%by weight or more, most preferably 0.3% by weight or more and usually10% by weight or less, preferably 8% by weight or less, particularlypreferably 5% by weight or less, most preferably 4% by weight or less.

In this connection, in the case of using a compound represented by theformula (4) of [A], the ratio of the acid anhydride and/or carbonicesters having an unsaturated bond in the molecule in the nonaqueouselectrolyte is more preferably 0.01 to 10% by weight, most preferably0.3 to 5% by weight. In the case of using a compound represented by theformula (5) of [A], the ratio of the acid anhydride and/or carbonicesters having an unsaturated bond in the molecule in the nonaqueouselectrolyte is more preferably 0.01 to 8% by weight. In the case ofusing a compound of [B], the ratio of the acid anhydride and/or carbonicesters having an unsaturated bond in the molecule in the nonaqueouselectrolyte is more preferably 0.01 to 8% by weight.

In the present invention, the main ingredients of the nonaqueouselectrolyte are, like usual nonaqueous electrolytes, a lithium salt andnonaqueous organic solvent that dissolves the salt.

The lithium salt is not particularly limited as far as it is a saltknown to be usable in this application and any one can be used.Specifically, the following may be mentioned.

-   1) Inorganic lithium salts: inorganic fluorides such as LiPF₆,    LiAsF₆, LiBF₄, and LiSbF₆, inorganic chlorides such as LiAlCl4,    perhalogenates such as LiClO₄, LiBrO₄, and LiIO₄.-   2) Organic lithium salts: fluorine-containing organic lithium salts,    e.g., perfluoroalkanesulfonates such as LiCF₃SO₃ and LiC₄F₉SO₃,    perfluoroalkanecarboxylates such as LiCF₃COO,    perfluoroalkanecarbonimides such as LiN(CF₃CO)₂,    perfluoroalkanesulfonimides such as LiN(CF₃SO₂)₂, LiN(C₂F₅SO₂)₂, and    LiN(CF₃SO₂)(C₄F₉SO₂), perfluoroalkanesulfonic methides such as    LiC(CF₃SO₂)₃, organic phosphates having perfluoroalkane group(s),    such as LiPF₄(CF₃), LiPF₄(C₂F₅), LiPF₄(CF₃SO₂)₂, and    LiPF₄(C₂F₅SO₂)₂, and organic borates having perfluoroalkane    group(s), such as LiBF₂(CF₃)₂, LiBF₂(C₂F₅)₂, LiBF₂(CF₃SO₂)₂, and    LiBF₂(C₂F₅SO₂)₂.

The lithium salts may be used singly or as a mixture of two or morethereof. Of these, suitably used is a lithium salt particularly selectedfrom the group consisting of LiPF₆, LiBF₄, LiCF₃SO₃, LiN(CF₃SO₂)₂, andLiN(C₂F₅SO₂)₂, which are easily soluble in a solvent and shows a highdegree of dissociation, and in particular, LiPF₆ or LiBF₄ is preferred.Moreover, the combined use of the inorganic lithium salt such as LiPF₆or LiBF₄ and the fluorine-containing organic lithium salt such asLiCF₃SO₃, LiN(CF₃SO₂)₂, or LiN(C₂F₅SO₂)₂ is preferred because gasgeneration during continuous charging is suppressed and deteriorationafter high-temperature storage is reduced. Particularly, preferred arethose wherein the content of LiPF₆ or LiBF₄ in the lithium salts in theelectrolyte is 70 to 98% by weight and the content of thefluorine-containing organic lithium salt selected from the groupconsisting of LiCF₃SO₃, LiN(CF₃SO₂)₂, and LiN(C₂F₅SO₂)₂ is 30 to 2% byweight.

In the case that the nonaqueous solvent comprises γ-butyrolactone in anamount of 55% by volume or more, it is preferred to use LiBF₄ in anamount of 50% by weight or more based on the total lithium salts.Particularly preferred are those wherein the content of LiBF₄ in thelithium salts is 50 to 95% by weight and the content of the lithium saltselected from the group consisting of LiPF₆, LiCF₃SO₃, LiN(CF₃SO₂)₂, andLiN(C₂F₅SO₂)₂ is 5 to 50% by weight.

The concentration of the lithium salt(s) in the nonaqueous electrolyteis in the range of usually 0.5 mol/liter or more, preferably 0.75mol/liter or more and usually 3 mol/liter or less, preferably 2mol/liter or less, more preferably 1.75 mol/liter or less. When theconcentration is too low, the electric conductivity of the electrolyteis insufficient. When the concentration is too high, the electricconductivity decreases due to increased viscosity and precipitation at alow temperature is apt to occur, so that cell performances tend todeteriorate.

The nonaqueous organic solvent can be suitably selected from among thosehitherto proposed as the solvents for nonaqueous electrolytes and used.For example, linear saturated carbonic esters, cyclic saturated carbonicesters, linear esters, cyclic esters (lactone compounds), linear ethers,cyclic ethers, sulfur-containing organic solvents, phosphorus-containingorganic solvents, and the like are mentioned.

Of these, usually preferred are linear saturated carbonic esters, cyclicsaturated carbonic esters, linear esters, cyclic esters, linear ethers,cyclic ethers, and phosphorus-containing organic solvents as solventsexhibiting a high conductivity. These compounds preferably have each 3to 9 carbon atoms in total.

Specific examples thereof include the following.

1) Linear saturated carbonic esters: There are mentioned linearsaturated carbonic esters containing alkyl groups each having 1 to 4carbon atoms, such as dimethyl carbonate, diethyl carbonate, di-n-propylcarbonate, ethyl methyl carbonate, methyl n-propyl carbonate, and ethyln-propyl carbonate. Of these, dimethyl carbonate, diethyl carbonate, orethyl methyl carbonate is preferred.

2) Cyclic saturated carbonic esters: There are mentioned cyclicsaturated carbonic esters containing an alkylene group having 2 to 4carbon atoms, such as ethylene carbonate, propylene carbonate, andbutylene carbonate. Of these, ethylene carbonate or propylene carbonateis preferred.

3) Linear ethers: There are mentioned dimethoxymethane,1,2-dimethoxyethane, 1,2-diethoxyethane, diethyl ether, and the like.

4) Cyclic ethers: There are mentioned tetrahydrofuran,2-methyltetrahydrofuran, 1,3-dioxolan, 4-methyl-1,3-dioxolan, and thelike.

5) Linear esters: There are mentioned methyl formate, methyl acetate,methyl propionate, methyl butyrate, and the like.

6) Cyclic esters: There are mentioned γ-butyrolactone, γ-valerolactone,and the like.

7) Phosphorus-containing organic solvent: There are mentioned trimethylphosphate, triethyl phosphate, dimethyl ethyl phosphate, methyl diethylphosphate, ethylene methyl phosphate, ethylene ethyl phosphate, and thelike.

These may be used singly or in combination of two or more thereof, butthe combined use of two or more compounds is preferred. For example, itis preferred to use a solvent having a high dielectric constant, such asa cyclic saturated carbonic ester or a cyclic ester, and a solventhaving a low viscosity, such as a linear saturated carbonic ester or alinear ester, in combination.

One of the preferred combinations of the nonaqueous solvents is acombination of mainly a cyclic saturated carbonic ester and a linearsaturated carbonic ester. In particular, preferred is a combination inwhich the total content of the cyclic saturated carbonic ester and thelinear saturated carbonic ester is 90% by volume or more, preferably 95%by volume or more and the volume ratio of the cyclic saturated carbonicesters and the linear saturated carbonic esters is 20:80 to 45:55. Thenonaqueous electrolyte obtained by incorporating a lithium salt and theaforementioned additives into the mixed solvent is preferable becauseimproved balance of cycle characteristics, large-current dischargecharacteristics, and suppression of gas generation.

The other preferred one among the nonaqueous solvents is a solventcontaining 60% by volume or more of an organic solvent selected from thegroup consisting of ethylene carbonate, propylene carbonate,γ-butyrolactone, and γ-valerolactone. The electrolyte obtained byincorporating a lithium salt and the aforementioned additives into themixed solvent reduces the evaporation of the solvent and the leakage ofthe liquid even when used at a high temperature. In particular,preferred is a combination in which the total content of ethylenecarbonate and γ-butyrolactone is 80% by volume or more, preferably 90%by volume or more, more preferably 95% by volume or more and the volumeratio of ethylene carbonate and γ-butyrolactone is 5:95 to 45:55 or acombination in which the total content of ethylene carbonate andpropylene carbonate is 80% by volume or more, preferably 90% by volumeor more, more preferably 95% by volume or more and the volume ratio ofethylene carbonate and propylene carbonate is 30:70 to 60:40. The use ofthe nonaqueous electrolyte obtained by incorporating a lithium salt andthe aforementioned additives into the mixed solvent is preferablebecause reduced gas generation and improved balance of cyclecharacteristics, large-current discharge characteristics, and the like.

Also, it is preferred to use a phosphorus-containing organic solvent asthe nonaqueous solvent. The incorporation of the phosphorus-containingorganic solvent in an amount of usually 10% by volume or more,preferably 10 to 80% by volume in a nonaqueous solvent can lower thecombustibility of the electrolyte. In particular, a combined use of thephosphorus-containing organic solvent and a nonaqueous solvent selectedfrom the group consisting of ethylene carbonate, propylene carbonate,γ-butyrolactone, γ-valerolactone, and dialkyl carbonate is preferredbecause of a good balance of cycle characteristics and large-currentdischarge characteristics.

Herein, the volume of the nonaqueous solvent is expressed by a measuredvalue at 25° C. but, when it is solid at 25° C., the volume is expressedby a measured value at the melting point.

The nonaqueous electrolyte according to the present invention maycomprise various auxiliary agents such as an overcharge inhibitor, anacid remover, a dehydrating agent, and the like.

Examples of the overcharge inhibitor include aromatic compounds such asbiphenyl, alkylbiphenyls, terphenyl, partially hydrogenated products ofterphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenylether, and dibenzofuran; partially fluorinated products of the abovearomatic compounds, such as 2-fluorobiphenyl, o-cyclohexylfluorobenzene,and p-cyclohexylfluorobenzene; fluorine-containing anisole compoundssuch as 2,4-difluoroanisole, 2,5-difluoroanisole, and2,6-difluoroanisole; and the like. The ratio of the overcharge inhibitorin the nonaqueous electrolyte is usually 0.1% by weight or more and 5%by weight or less. The incorporation of the overcharge inhibitor caninhibit the burst and firing of the battery at overcharge or the likesituation.

Examples of the other auxiliary agents include carbonic ester compoundssuch as fluoroethylene carbonate, trifluoropropylene carbonate,erythritan carbonate, and spiro-bis-dimethylene carbonate; carboxylicesters such as vinyl acetate, divinyl adipate, allyl acetate;sulfur-containing compounds such as dimethyl sulfite, ethylene sulfite,1,3-propanesultone, 1,4-butanesultone, methyl methanesulfonate,2-propynyl methanesulfonate, sulfolane, sulfolene, dimethyl sulfone,divinyl sulfone, tetramethylthiuram monosulfide, diphenyl disulfide, and1,4-butanediol dimethanesulfonate: nitrogen-containing compounds such as1-methyl-2-pyrrolidinone, 1-methyl-2-piperidone,3-methyl-2-oxazolidinone, 1,3-dimethyl-2-imidazolidinone, andN-methylsuccinimide; hydrocarbon compounds such as heptane, octane, andcycloheptane; and the like.

The ratio of these auxiliary agents in the nonaqueous electrolyte isusually 0.1% by weight or more and 5% by weight or less. Theincorporation of these auxiliary agents can improve capacity-retentioncharacteristics after high-temperature storage and cyclecharacteristics.

The nonaqueous electrolyte according to the invention can be prepared bydissolving a lithium salt, aforementioned additives, a compound selectedfrom acid anhydrides and carbonic esters having an unsaturated bond,and, if necessary, the other compound in a nonaqueous organic solvent.At the preparation of the nonaqueous electrolyte, individual rawmaterials are preferably dehydrated beforehand. It is suitable todehydrate them to the water content of usually 50 ppm, preferably 30ppm.

The nonaqueous electrolyte according to the invention is suitable foruse as an electrolyte for secondary battery, especially for lithiumsecondary battery. The following will describe the lithium secondarybattery according to the invention employing the electrolyte.

The lithium secondary battery according to the invention is the same asthe hitherto known lithium secondary battery with the exception of theelectrolyte, and usually, a positive electrode and a negative electrodeare placed in a case through a porous film which is impregnated with thenonaqueous electrolyte according to the invention. Therefore, the formof the secondary battery according to the invention is no particularlimitation, and the battery may be in any of a cylindrical shape, aprismatic shape, a laminate shape, a coin shape, a large one, etc. Thelithium secondary battery according to the invention can prevent theabnormal working of a circuit breaker in a continuous charge state ofthe battery equipped with a circuit breaker which works when the innerpressure of the battery increases at an abnormal situation such asovercharge. Moreover, in the battery whose outer package material ismainly metal aluminum or an aluminum alloy, there is apt to occur aproblem of battery swelling to be induced by the increase of innerpressure of the battery but the lithium secondary battery according tothe invention can prevent the occurrence of such a problem because ofreduced gas generation.

As the negative active material, use can be made of carbonaceousmaterials which can intercalate and release lithium; metal oxidematerials which can intercalate and release lithium; such as tin oxideand silicon oxide; lithium metal; various lithium alloys; and the like.These negative active materials may be used singly or as a mixture oftwo or more thereof.

As the carbonaceous materials capable of intercalating and releasinglithium, preferred are graphite and materials obtained by covering thesurface of graphite with a carbon more amorphous than graphite.

As graphite, preferred are those having a “d” value (interlayerdistance) for lattice plane (002) determined by X-ray diffractionanalysis based on the method of Gakushin (Japan Society for thePromotion of Science) of 0.335 to 0.338 nm, particularly 0.335 to 0.337nm. The crystallite size “Lc” determined by X-ray diffraction analysisbased on the method of Gakushin is usually 30 nm or larger, preferably50 nm or larger, and particularly preferably 100 nm or larger. The ashcontent is usually 1% by weight or less, preferably 0.5% by weight orless, and particularly preferably 0.1% by weight or less.

Preferred materials obtained by covering the surface of graphite with acarbon more amorphous than graphite are those in which a graphitematerial having a “d” value for lattice plane (002) determined by X-raydiffraction analysis of 0.335 to 0.338 nm is used as a nucleus materialand a carbonaceous material having a “d” value for lattice plane (002)determined by X-ray diffraction analysis larger than the value of thenucleus material is attached to the surface and the ratio of the nucleusmaterial to the carbonaceous material having a “d” value for latticeplane (002) determined by X-ray diffraction analysis larger than thevalue of the nucleus material is 99/1 to 80/20 by weight. By the use ofthe material, a negative electrode having high capacity and hardlyreactive with the electrolyte can be produced.

The particle size of the carbonaceous materials is, as a median diameterdetermined by the laser diffraction-scattering method, usually 1 μm ormore, preferably 3 μm or more, more preferably 5 μm or more, mostpreferably 7 μm or more and usually 100 μm or less, preferably 50 μm orless, more preferably 40 μm or less, most preferably 30 μm or less.

The specific surface area of the carbonaceous material determined by theBET method is usually 0.3 m²/g or more, preferably 0.5 m²/g or more,more preferably 0.7 m²/g or more, most preferably 0.8 m²/g or more andusually 25.0 m²/g or less, preferably 20.0 m²/g or less, more preferably15.0 m²/g or less, most preferably 10.0 m²/g or less.

Moreover, the carbonaceous material preferably has an “R” value(=I_(B)/I_(A)) determined by the ratio of I_(B) to I_(A) of 0.01 to 0.7,wherein “I_(A)” is an intensity of peak “P_(A)” within the range of 1570to 1620 cm⁻¹ and “I_(B)” is an intensity of peak “P_(B)” within therange of 1300 to 1400 cm⁻¹ when analyzed by raman spectrometry using anargon ion laser. A half-band width of the peak within the range of 1570to 1620 cm⁻¹ is preferably 26 cm⁻¹ or less, and more preferably 25 cm⁻¹or less.

As the positive active material, there are mentioned lithium-transitionmetal compound oxides such as lithium cobalt oxide, lithium nickeloxide, and lithium manganese oxide, which are capable of intercalatingand releasing lithium.

As binders for binding the active materials, any materials stable tosolvents to be used at the production of electrodes and the electrolytecan be employed. Examples thereof include fluorine polymers such aspolyvinylidene fluoride and polytetrafluoroethylene, polyolefins such aspolyethylene and polypropylene, polymers having an unsaturated bond andcopolymers thereof, such as styrene-butadiene rubbers, isoprene rubbers,butadiene rubbers, and acrylic polymers and copolymers thereof, such asethylene-acrylic acid copolymers and ethylene-methacrylic acidcopolymers.

In order to enhance mechanical strength and electric conductivity, athickener, a conductive material, a filler, and the like may beincorporated.

Examples of the thickener include carboxymethyl cellulose, methylcellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol,starch oxide, starch phosphate and casein.

Examples of the conductive material include metal materials such ascopper and nickel or carbonaceous materials such as graphite and carbonblack.

The production of the electrodes may be effected according to a usualmanner. For example, the negative or positive active material may beadded with a binder, thickener, conductive material, solvent and thelike to thereby prepare a slurry, and the resulting slurry is appliedonto a current collector, which is followed by drying and then pressingto form an electrode.

The density of the negative active material layer after drying andpressing is usually 1.45 g/cm³ or more, preferably 1.55 g/cm³ or more,particularly preferably 1.60 g/cm³ or more. A higher density of thenegative active material layer results in an increased capacity of thebattery and hence is preferred. Moreover, the density of the positiveactive material layer after drying and pressing is usually 3.0 g/cm³.When the density of the positive active material layer is too low, aninsufficient capacity of the battery is obtained.

Various materials can be used as the current collector but a metal orits alloy is usually employed. Examples of the current collector for thenegative electrode include copper, nickel, stainless steel, and thelike, and preferred is copper. Examples of the current collector for thepositive electrode include metals such as aluminum, titanium, tantalum,and alloys thereof. Of these, preferred is aluminum or an alloy thereof.

A porous film is interposed between the positive electrode and thenegative electrode in order to prevent short-circuit. The material andshape of the porous film are not specifically limited as far as the filmis excellent in stability to the electrolytic solution and in retentionof the liquid. Preferred is a porous sheet or non-woven fabric, made ofa polyolefin such as polyethylene or polypropylene.

The material of the outer package of the battery for use in theinvention is also optional, and nickel-plated iron, stainless steel,aluminum or its alloys, nickel, titanium, and the like may be employed.

EXAMPLES

The following will further describe specific embodiments of theinvention with reference to Examples, but the invention should not beconstrued to be limited by these Examples unless it exceeds the gist.

Example 1

[Production of Positive Electrode]

A positive electrode was obtained by mixing 90% by weight of lithiumnickel compound oxide (LiNi_(0.82)Co_(0.15)Al_(0.03)O₂) , 5% by weightof polyvinylidene fluoride (PVdF), and 5% by weight of acetylene black,adding N-methylpyrrolidone to form a slurry, and applying the slurryonto both surfaces of a current collector made of aluminum, followed bydrying.

[Production of Negative Electrode]

A negative electrode was obtained by mixing 90% by weight of graphitepowder and 10% by weight of PVdF, adding N-methylpyrrolidone to form aslurry, and applying the slurry onto one surface of a current collectormade of copper, followed by drying.

[Blending of Electrolyte]

A base electrolyte was prepared by adding 2 parts by weight of vinylenecarbonate to 100 parts by weight of a mixed solvent of ethylenecarbonate and ethyl methyl carbonate (mixing ratio of 1:3 by volume)containing LiPF₆ in a ratio of 1.25 mol/L. To the base electrolyte wasadded 1 part by weight of 1,2,4-butanetriol trimethanesulfonate tothereby form an electrolyte.

[Production of Lithium Secondary Battery]

The above positive electrode, negative electrode, and a biaxiallyoriented porous polyethylene film having a film thickness of 16 μm, avoid content of 45%, and an average pore size of 0.05 μm were eachcoated and impregnated with the above electrolyte and then they werelaminated in the order of the negative electrode, the separator, thepositive electrode, the separator, and the negative electrode.

The cell element thus obtained was first put between PET films and then,while the terminals of the positive electrode and the negative electrodewas provided in an extended condition toward a laminate film obtained bycovering an aluminum layer with resin layers, was vacuum-sealed toprepare a sheet-form lithium secondary battery. In order to furtherenhance the adhesiveness between the electrodes, the sheet-form batterywas put between silicone rubbers and glass plates and then pressurizedat 0.35 kg/cm². FIG. 1 shows a schematic cross-sectional view.

[Capacity Evaluation]

The discharge capacity of lithium nickel compound oxide per 1 hour wasconsidered as 180 mAh/g and a discharge rate 1 C was determined based onthe capacity and the weight of positive active material of the lithiumsecondary battery for evaluation to set a rate. Then, the battery wascharged at 0.2 C to 4.2V and then discharged at 0.2 C to 3V to conductinitial formation. Thereafter, the battery was charged at 0.5 C to 4.2Vand then again discharged at 0.2 C to 3V to determine a dischargecapacity at 0.2 C. In this connection, the cut current at the chargingwas set at 0.05 C.

[Storage Characteristic Evaluation]

The battery after subjected to the capacity evaluation test was chargedat 0.5 C to 4.2V and was stored in a constant-temperature bath at 85° C.for 1 day. Thereafter, the amount of gas generation was determined byimmersing the battery into an ethanol bath to measure buoyant force(Archimedean principle). In addition, for evaluating the degree ofcapacity deterioration after the storage, the battery was charged at 0.5C to 4.2V and then discharged at 0.2 C to measure a discharge capacityat 0.2 C after the storage, and a capacity recovery was determinedaccording to the following equation. The results are shown in Table 1.Capacity recovery (%)=Discharge capacity at 0.2 C after storage(mAh/g)/Discharge capacity at 0.2 C (mAh/g)

Example 2

A lithium secondary battery was prepared in the same manner as inExample 1 with the exception of the use of an electrolyte in which theamount of 1,2,4-butanetriol trimethanesulfonate added was changed to 3parts by weight, and battery characteristic tests the same as in Example1 were conducted. The results are shown in Table 1.

Example 3

A lithium secondary battery was prepared in the same manner as inExample 1 with the exception of the use of an electrolyte in which theamount of 1,2,4-butanetriol trimethanesulfonate added was changed to 5parts by weight, and battery characteristic tests the same as in Example1 were conducted. The results are shown in Table 1.

Referential Example 1

A lithium secondary battery was prepared in the same manner as inExample 1 with the exception of the use of an electrolyte in which1,2,4-butanetriol trimethanesulfonate was added in an amount of 1 partby weight per 100 parts by weight of a mixed solvent of ethylenecarbonate and diethyl carbonate (mixing ratio of 1:1 by volume)containing LiPF₆ in a ratio of 1.0 mol/L, and battery characteristictests the same as in Example 1 were conducted. The results are shown inTable 1.

Comparative Example 1

A lithium secondary battery was prepared in the same manner as inExample 1 with the exception of the use of an electrolyte in which1,2,4-butanetriol trimethanesulfonate was not added, and batterycharacteristic tests the same as in Example 1 were conducted. Theresults are shown in Table 1. The capacity recovery is low and also alarge amount of gas is generated. Thus, it is understood that storagecharacteristics are very poor.

Comparative Example 2

A lithium secondary battery was prepared in the same manner as inExample 1 with the exception of the use of an electrolyte in which1,4-butanediol dimethanesulfonate was added instead of 1,2,4-butanetrioltrimethanesulfonate, and battery characteristic tests the same as inExample 1 were conducted. The results are shown in Table 1. Animprovement in the capacity recovery is observed but an effect tosuppress the gas generation is insufficient.

Example 4

[Production of Positive Electrode]

A positive electrode was obtained by mixing 90% by weight of lithiumcobalt compound oxide (LiCoO₂), 5% by weight of polyvinylidene fluoride(PVdF), and 5% by weight of acetylene black, adding N-methylpyrrolidonethereto to form a slurry, and applying the slurry onto both surfaces ofa current collector made of aluminum, followed by drying.

[Production of Negative Electrode]

A negative electrode was obtained by mixing 87.4% by weight of graphitepowder, 9.7% by weight of PVdF, and 2.9% by weight of acetylene black,adding N-methylpyrrolidone thereto to form a slurry, and applying theslurry onto one surface of a current collector made of copper, followedby drying.

[Blending of Electrolyte]

A base electrolyte was prepared by adding 2 parts by weight of vinylenecarbonate to 100 parts by weight of a mixed solvent of ethylenecarbonate and ethyl methyl carbonate (mixing ratio of 1:3 by volume)containing LiPF₆ in a ratio of 1.25 mol/L. To the base electrolyte wasadded 1 part by weight of 1,2,4-butanetriol trimethanesulfonate tothereby form an electrolyte.

[Production of Lithium secondary Battery]

The above positive electrode, negative electrode, and a biaxiallyoriented porous polyethylene film having a film thickness of 16 μm, avoid content of 45%, and an average pore size of 0.05 μm were eachcoated and impregnated with the above electrolyte and then they werelaminated in the order of the negative electrode, the separator, thepositive electrode, the separator, and the negative electrode. The cellelement thus obtained was first put between PET films and then, whilethe terminals of the positive electrode and the negative electrode wasprovided in an extended condition toward a laminate film obtained bycovering both surfaces of an aluminum layer with resin layers, wasvacuum-sealed to prepare a sheet-form lithium secondary battery. Inorder to further enhance the adhesiveness between the electrodes, thesheet-form battery was put between silicone rubber and glass plat andthen pressurized at 0.35 kg/cm².

[Capacity Evaluation]

The discharge capacity of lithium cobalt compound oxide per 1 hour wasconsidered as 138 mAh/g and a discharge rate 1 C was determined based onthe capacity and the weight of positive active material of the lithiumsecondary battery for evaluation to set a rate. Then, the battery wascharged at 0.2 C to 4.2V and then discharged at 0.2 C to 3V to conductinitial formation. Thereafter, the battery was charged at 0.5 C to 4.2Vand then again discharged at 0.2 C to 3V to determine a dischargecapacity at 0.2 C. In this connection, the cut current at the chargingwas set at 0.5 C.

[Storage Characteristic Evaluation]

The battery after subjected to the capacity evaluation test was chargedat 0.5 C to 4.2V and was stored in a constant-temperature bath at 85° C.for 1 day. Thereafter, the amount of gas generation was determined byimmersing the battery into an ethanol bath to measure buoyant force(Archimedean principle). In addition, for evaluating the degree ofcapacity deterioration after the storage, the battery was charged at 0.5C to 4.2V and then discharged at 0.2 C to measure a discharge capacityat 0.2 C after the storage, and a capacity recovery was determinedaccording to the aforementioned equation. The results are shown in Table1.

Comparative Example 3

A lithium secondary battery was prepared in the same manner as inExample 4 with the exception of the use of an electrolyte in which1,2,4-butanetriol trimethanesulfonate was not added, and batterycharacteristic tests the same as in Example 4 were conducted. Theresults are shown in Table 1. Since lithium cobalt compound oxide isused as the positive active material, the amount of gas generation afterthe storage is on a low level but the capacity recovery is insufficient.TABLE 1 Capacity Amount of gas Added amount Positive Electrolyterecovery generation Additive part by weight electrode composition (%)(cc) Example 1 1,2,4-butanetriol 1 lithium nickel 1.25M LiPF₆/ 83.0 0.19trimethanesulfonate compound oxide EC + EMC(1:3) + VC2% Example 21,2,4-butanetriol 3 lithium nickel 1.25M LiPF₆/ 83.4 0.15trimethanesulfonate compound oxide EC + EMC(1:3) + VC2% Example 31,2,4-butanetriol 5 lithium nickel 1.25M LiPF₆/ 82.9 0.13trimethanesulfonate compound oxide EC + EMC(1:3) + VC2% Referential1,2,4-butanetriol 1 lithium nickel 1.0M LiPF₆/ 84.2 0.20 Example 1trimethanesulfonate compound oxide EC + DEC(1:1) Comparative none —lithium nickel 1.25M LiPF₆/ 80.6 0.79 Example 1 compound oxide EC +EMC(1:3) + VC2% Comparative 1,4-butanediol 1 lithium nickel 1.25M LiPF₆/83.0 0.38 Example 2 dimethanesulfonate compound oxide EC + EMC(1:3) +VC2% Example 4 1,2,4-butanetriol 1 lithium cobalt 1.25M LiPF₆/ 81.7 0.06trimethanesulfonate compound oxide EC + EMC(1:3) + VC2% Comparative none— lithium cobalt 1.25M LiPF₆/ 77.8 0.11 Example 3 compound oxide EC +EMC(1:3) + VC2%

Example 5

A lithium secondary battery was prepared in the same manner as inExample 4 with the exception of the use of an electrolyte in which1,2,4-butanetriol trimethanesulfonate was added in an amount of 1 partby weight per 100 parts by weight of a mixed solvent of ethylenecarbonate and ethyl methyl carbonate (mixing ratio of 1:3 by volume)containing LiPF₆ in a ratio of 1 mol/L, and a capacity evaluation testthe same as in Example 4 was conducted.

Then, the battery was placed in a constant-temperature bath at 60° C.and was charged at a constant current at 0.7 C and, when the voltagereached 4.25V, switched to a constant-voltage charging. After chargedfor 7 days, the battery was immersed into an ethanol bath to measurebuoyant force and the amount of gas generation was calculated from thebuoyant force. The results are shown in Table 2.

Comparative Example 4

A lithium secondary battery was prepared in the same manner as inExample 5 with the exception of the use of an electrolyte in which1,3-propanesultone was added instead of 1,2,4-butanetrioltrimethanesulfonate, and battery characteristic tests the same as inExample 4 were conducted. The results are shown in Table 2.

Comparative Example 5

A lithium secondary battery was prepared in the same manner as inExample 5 with the exception of the use of an electrolyte in which1,2,4-butanetriol trimethanesulfonate was not added, and batterycharacteristic tests the same as in Example 4 were conducted. Theresults are shown in Table 2. TABLE 2 Amount of gas Added amountPositive Electrolyte generation after 7 days Additive part by weightelectrode composition of continuous charging (ml) Example 51,2,4-butanetriol 1 lithium cobalt 1M LiPF₆/ 0.54 trimethanesulfonatecompound oxide EC + EMC(1:3) + VC2% Comparative 1,3-propanesultone 1lithium cobalt 1M LiPF₆/ 0.66 Example 4 compound oxide EC + EMC(1:3) +VC2% Comparative none — lithium cobalt 1M LiPF₆/ 0.73 Example 5 compoundoxide EC + EMC(1:3) + VC2%

Example 6

A lithium secondary battery was prepared in the same manner as inExample 1 with the exception of the use of an electrolyte in which 1part by weight of 1,4-butanediol bis(2,2,2-trifluoroethanesulfonate) wasadded instead of 1 part by weight of 1,2,4-butanetrioltrimethanesulfonate, and battery characteristic tests the same as inExample 1 were conducted. The results are shown in Table 3.

Example 7

A lithium secondary battery was prepared in the same manner as inExample 6 with the exception of the use of an electrolyte in which theamount of 1,4-butanediol bis(2,2,2-trifluoroethanesulfonate) added waschanged to 3 parts by weight, and battery characteristic tests the sameas in Example 1 were conducted. The results are shown in Table 3.

Example 8

A lithium secondary battery was prepared in the same manner as inExample 6 with the exception of the use of an electrolyte in which theamount of 1,4-butanediol bis(2,2,2-trifluoroethanesulfonate) added waschanged to 5 parts by weight, and battery characteristic tests the sameas in Example 1 were conducted. The results are shown in Table 3.

Referential Example 2

A lithium secondary battery was prepared in the same manner as inReferential Example 1 with the exception of the use of an electrolyte inwhich 1 part by weight of 1,4-butanediolbis(2,2,2-trifluoroethanesulfonate) was added instead of 1 part byweight of 1,2,4-butanetriol trimethanesulfonate, and batterycharacteristic tests the same as in Example 1 were conducted. Theresults are shown in Table 3.

Example 9

A lithium secondary battery was prepared in the same manner as inExample 4 with the exception of the use of an electrolyte in which 1part by weight of 1,4-butanediol bis(2,2,2-trifluoroethanesulfonate) wasadded instead of 1 part by weight of 1,2,4-butanetrioltrimethanesulfonate was used, and battery characteristic tests the sameas in Example 4 were conducted. The results are shown in Table 3. TABLE3 Capacity Amount of gas Added amount Positive Electrolyte recoverygeneration Additive part by weight electrode composition (%) (cc)Example 6 1,4-butanediol bis(2,2,2- 1 lithium nickel 1.25M LiPF₆/ 83.40.20 trifluoroethanesulfonate) compound oxide EC + EMC(1:3) + VC2%Example 7 1,4-butanediol bis(2,2,2- 3 lithium nickel 1.25M LiPF₆/ 82.70.20 trifluoroethanesulfonate) compound oxide EC + EMC(1:3) + VC2%Example 8 1,4-butanediol bis(2,2,2- 5 lithium nickel 1.25M LiPF₆/ 82.40.17 trifluoroethanesulfonate) compound oxide EC + EMC(1:3) + VC2%Referential 1,4-butanediol bis(2,2,2- 1 lithium nickel 1.0M LiPF₆/ 83.80.21 Example 2 trifluoroethanesulfonate) compound oxide EC + DEC(1:1)Example 9 1,4-butanediol bis(2,2,2- 1 lithium cobalt 1.25M LiPF₆/ 80.60.08 trifluoroethanesulfonate) compound oxide EC + EMC(1:3) + VC2%

Example 10

A lithium secondary battery was prepared in the same manner as inExample 5 with the exception of the use of an electrolyte in which 1part by weight of 1,4-butanediol bis(2,2,2-trifluoroethanesulfonate) wasadded instead of 1 part by weight of 1,2,4-butanetrioltrimethanesulfonate, and battery characteristic tests the same as inExample 4 were conducted. The amount of gas generation after 7 days ofcontinuous charging was 0.46 ml.

Example 11

A base electrolyte (I) was prepared by adding 2 parts by weight ofvinylene carbonate to 100 parts by weight of a mixed solvent of ethylenecarbonate and ethyl methyl carbonate (mixing ratio of 1:3 by volume)containing LiPF₆ in a ratio of 1 mol/L. To the base electrolyte wasadded 1 part by weight of trimethylsilyl methanesulfonate to therebyform an electrolyte. Using the resulting electrolyte, a lithiumsecondary battery was prepared in the same manner as in Example 4.

[Capacity Evaluation]

The discharge capacity of lithium cobalt oxide per 1 hour was consideredas 140 mAh/g and a discharge rate 1 C was determined based on thecapacity and the weight of positive active material of the lithiumsecondary battery for evaluation to set a rate. Then, in aconstant-temperature bath at 25° C., the battery was charged at 0.2 C to4.2V and then discharged at 0.2 C to 3V to conduct initial formation.Thereafter, the battery was charged at 0.7 C to 4.2V and then againdischarged at 1 C to 3V to determine an initial discharge capacity. Inthis connection, the cut current at the charging was set at 0.05 C.

[Continuous Charge Characteristic Evaluation]

(1) Amount of Gas Generation

The battery after subjected to the capacity evaluation test was placedin a constant-temperature bath at 60° C. and was charged at a constantcurrent at 0.7 C and, when the voltage reached 4.25V, switched toconstant-voltage charging. After 7 days of charging, the battery wasimmersed into an ethanol bath to measure buoyant force and the amount ofgas generation was calculated from the buoyant force.

(2) Recovered 0.2 C Capacity

In order to evaluate the degree of capacity deterioration after thecontinuous charging, after the measurement of the amount of gasgeneration, the battery was first discharged at 0.2 C to 3V and thencharged at 0.7 C to 4.2V. Furthermore, it was discharged at 0.2 C and adischarge capacity at that time was measured. The larger the value is,the smaller the deterioration of the battery is.

[Cycle Characteristic Evaluation]

Charging and discharging, wherein the battery after subjected to thecapacity evaluation test was charged at 0.7 C to 4.2V (cut current 0.05C) in a constant-temperature bath at 25° C. and then discharged at 1 Cto 3V, were repeated. 1 C discharge capacity after 200 cycles wasmeasured and the capacity retention after 200 cycles was determinedaccording to the following equation. The larger the value is, thesmaller the deterioration of the battery during the charging/dischargingcycles is.Capacity retention (%) after 200 cycles=Discharge capacity after 200cycles (mAh/g)/Initial discharge capacity (mAh/g)

The results are shown in Table 4.

Example 12

Using an electrolyte obtained by adding 3 parts by weight oftrimethylsilyl methanesulfonate to 102 parts by weight of the baseelectrolyte (I), a lithium secondary battery was prepared in the samemanner as in Example 11, and continuous charge characteristicsevaluation was conducted. The results are shown in Table 4.

Comparative Example 6

Using the base electrolyte (I) itself, a lithium secondary battery wasprepared in the same manner as in Example 11, and continuous chargecharacteristics evaluation and cycle characteristic evaluation wereconducted. The results are shown in Table 4.

Comparative Example 7

Using an electrolyte obtained by adding 3 parts by weight of methylmethanesulfonate to 102 parts by weight of the base electrolyte (I), alithium secondary battery was prepared in the same manner as in Example11, and continuous charge characteristic evaluation was conducted. Theresults are shown in Table 4. TABLE 4 After 7 days of continuouscharging Recovered 0.2C Capacity Added amount Electrolyte Amount of gascapacity retention after Additive part by weight composition generation(ml) (mAh/g) 200 cycles (%) Example 11 trimethylsilyl 1 1M LiPF₆/ 0.51122.2 89.4 methanesulfonate EC + EMC(1:3) + VC2% Example 12trimethylsilyl 3 1M LiPF₆/ 0.44 120.9 — methanesulfonate EC + EMC(1:3) +VC2% Comparative none — 1M LiPF₆/ 0.73 117.8 78.9 Example 6 EC +EMC(1:3) + VC2% Comparative methyl 3 1M LiPF₆/ 0.71 114.9 — Example 7methanesulfonate EC + EMC(1:3) + VC2%

Example 13

A base electrolyte (II) was prepared by adding 2 parts by weight ofvinylene carbonate to 100 parts by weight of a mixed solvent of ethylenecarbonate and γ-butyrolactone (mixing ratio of 1:3 by volume) containingLiPF₆ in a ratio of 1 mol/L. To the base electrolyte was added 1 part byweight of trimethylsilyl methanesulfonate to thereby form anelectrolyte.

Using the resulting electrolyte, a lithium secondary battery wasprepared in the same manner as in Example 11, and cycle characteristicevaluation was conducted. The results are shown in Table 5.

Example 14

A lithium secondary battery was prepared in the same manner as inExample 13 as in Example 11 with the exception of the use of anelectrolyte in which 3 parts by weight of trimethylsilylmethanesulfonate was added to 102 parts by weight of the baseelectrolyte (II), and cycle characteristic evaluation was conducted. Theresults are shown in Table 5.

Comparative Example 8

A lithium secondary battery was prepared in the same manner as inExample 11 using the base electrolyte (II) itself, and cyclecharacteristic evaluation was conducted. The results are shown in Table5.

Comparative Example 9

A lithium secondary battery was prepared in the same manner as inExample 11 using an electrolyte obtained by adding 1 part by weight ofmethyl methanesulfonate to 102 parts by weight of the base electrolyte(II), and cycle characteristic evaluation was conducted. The results areshown in Table 5. TABLE 5 Added amount Electrolyte Capacity retentionAdditive part by weight composition after 200 cycles (%) Example 13trimethylsilyl 1 1M LiPF₆/ 87.2 methanesulfonate EC + GBL(1:3) + VC2%Example 14 trimethylsilyl 3 1M LiPF₆/ 86.6 methanesulfonate EC +GBL(1:3) + VC2% Comparative none — 1M LiPF₆/ 82.5 Example 8 EC +GBL(1:3) + VC2% Comparative methyl 1 1M LiPF₆/ 84.5 Example 9methanesulfonate EC + GBL(1:3) + VC2%

Example 15

A base electrolyte (III) was prepared by dissolving LiPF₆ in a ratio of1 mol/L into a mixed solvent of ethylene carbonate and ethyl methylcarbonate (mixing ratio of 1:3 by volume). To the base electrolyte wereadded 1 part by weight of 1,4-thioxane-1,1-dioxide and 2 parts by weightof vinylene carbonate to thereby form an electrolyte.

Using the resulting electrolyte, a lithium secondary battery wasprepared in the same manner in Example 4, and high-temperature storagecharacteristic evaluation and continuous charge characteristicevaluation were conducted.

[Capacity Evaluation]

The discharge capacity of lithium cobalt oxide per 1 hour was consideredas 140 mAh/g and a discharge rate 1 C was determined based on thecapacity and the weight of positive active material of the lithiumsecondary battery for evaluation to set a rate. Then, in aconstant-temperature bath at 25° C., the battery was charged at 0.2 C to4.2V and then discharged at 0.2 C to 3V to conduct initial formation.Thereafter, the battery was charged at 0.7 C to 4.2V and then againdischarged at 0.2 C to 3V to determine an initial discharge capacity.The cut current at the charging was set at 0.05 C.

[High-Temperature Storage Characteristic Evaluation]

The battery after subjected to the capacity evaluation test was chargedat 0.7 C to 4.2V (cut current 0.05 C) in a constant-temperature bath at25° C. and then stored in a constant-temperature bath at 85° C. for 1day. Thereafter, the battery was thoroughly cooled and then dischargedat 0.2 C to 3V to determine a residual capacity after thehigh-temperature storage. Then, the battery was charged at 0.7 C to 4.2V(cut current 0.05 C) and then discharged at 0.2 C to 3V to measure arecovered capacity after the high-temperature storage.

According to the following equation, residual capacity retention andrecovered capacity retention after the high-temperature storage weredetermined. The larger these values are, the smaller the self-dischargeand the deterioration of the battery after the high-temperature storageare.Residual capacity retention (%) after high-temperature storage=Residualcapacity after high-temperature storage/Initial discharge capacity×100Recovered capacity retention (%) after high-temperaturestorage=Recovered capacity after high-temperature storage/Initialdischarge capacity×100[Continuous Charge Characteristic Evaluation]

The battery after subjected to the capacity evaluation test was placedin a constant-temperature bath at 60° C. and was charged at a constantcurrent at 0.7 C and, when the voltage reached 4.25V, switched toconstant-voltage charging. After 7 days of charging, in order toevaluate the degree of capacity deterioration after the continuouscharging, the battery was first discharged at 0.2 C to 3V and thencharged at 0.7 C to 4.2V. Furthermore, it was discharged at 0.2 C to 3Vand a discharge capacity at that time (recovered capacity) was measured.

According to the following equation, a recovered capacity retentionafter the continuous charging was determined. The larger the value is,the smaller the deterioration of the battery is.Recovered capacity retention (%) after 7 days of continuouscharging=Recovered capacity after 7 days of continuous charging/Initialdischarge capacity×100

The results are shown in Table 6.

Example 16

Using an electrolyte obtained by adding 1 part by weight of1,4-thioxane-1,1-dioxide and 1 part by weight of vinylene carbonate to100 parts by weight of the base electrolyte (III), a lithium secondarybattery was prepared in the same manner as in Example 15, andhigh-temperature storage characteristic evaluation and continuous chargecharacteristic evaluation were conducted. The results are shown in Table6.

Example 17

Using an electrolyte obtained by adding 1 part by weight of1,4-thioxane-1,1-dioxide and 0.5 part by weight of vinylethylenecarbonate to 100 parts by weight of the base electrolyte (III), alithium secondary battery was prepared in the same manner as in Example15, and high-temperature storage characteristic evaluation andcontinuous charge characteristic evaluation were conducted. The resultsare shown in Table 6.

Comparative Example 10

Using the base electrolyte (III) itself, a lithium secondary battery wasprepared in the same manner as in Example 15, and high-temperaturestorage characteristic evaluation and continuous charge characteristicevaluation were conducted. The results are shown in Table 6.

Comparative Example 11

Using an electrolyte obtained by adding 1 part by weight of1,4-thioxane-1,1-dioxide to 100 parts by weight of the base electrolyte(III), a lithium secondary battery was prepared in the same manner as inExample 15, and high-temperature storage characteristic evaluation andcontinuous charge characteristic evaluation were conducted. The resultsare shown in Table 6.

Example 18

Using an electrolyte obtained by adding 3 parts by weight of1,4-thioxane-1,1-dioxide and 2 parts by weight of vinylene carbonate to100 parts by weight of the base electrolyte (III), a lithium secondarybattery was prepared in the same manner as in Example 15, andhigh-temperature storage characteristic evaluation and continuous chargecharacteristic evaluation were conducted. The results are shown in Table6.

Comparative Example 12

Using an electrolyte obtained by adding 3 parts by weight of1,4-thioxane-1,1-dioxide to 100 parts by weight of the base electrolyte(III), a lithium secondary battery was prepared in the same manner as inExample 15, and high-temperature storage characteristic evaluation andcontinuous charge characteristic evaluation were conducted. The resultsare shown in Table 6.

Example 19

Using an electrolyte obtained by adding 0.5 part by weight of1,4-thioxane-1,1-dioxide and 2 parts by weight of vinylene carbonate to100 parts by weight of the base electrolyte (III), a lithium secondarybattery was prepared in the same manner as in Example 15, andhigh-temperature storage characteristic evaluation and continuous chargecharacteristic evaluation were conducted. The results are shown in Table6.

Comparative Example 13

Using an electrolyte obtained by adding 2 parts by weight of vinylenecarbonate to 100 parts by weight of the base electrolyte (III), alithium secondary battery was prepared in the same manner as in Example15, and high-temperature storage characteristic evaluation andcontinuous charge characteristic evaluation were conducted. The resultsare shown in Table 6.

Example 20

A base electrolyte (IV) was prepared by dissolving LiPF₆ in a ratio of 1mol/L into a mixed solvent of ethylene carbonate (EC) andγ-butyrolactone (GBL) (mixing ratio of 1:3 by volume). Using anelectrolyte obtained by adding 1 part by weight of1,4-thioxane-1,1-dioxide and 2 parts by weight of vinylene carbonate tothe base electrolyte (IV), a lithium secondary battery was prepared inthe same manner in Example 15, and high-temperature storagecharacteristic evaluation and continuous charge characteristicevaluation were conducted. The results are shown in Table 6. TABLE 6Residual Recovered Recovered Additive Unsaturated carbonate capacitycapacity capacity retention Content Content retention after retentionafter after 7 days of part by part by Electrolyte high-temperaturehigh-temperature continuous Compound weight Compound weight compositionstorage (%) storage (%) charging (%) Example 15 1,4-thioxane- 1 vinylene2 1M LiPF₆/ 85.9 93.1 88.2 1,1-dioxide carbonate EC + EMC(1:3) Example16 1,4-thioxane- 1 vinylene 1 1M LiPF₆/ 86.3 92.1 89.0 1,1-dioxidecarbonate EC + EMC(1:3) Example 17 1,4-thioxane- 1 vinyl-ethylene 0.5 1MLiPF₆/ 86.0 91.1 87.7 1,1-dioxide carbonate EC + EMC(1:3) Comparativenone — none — 1M LiPF₆/ 81.7 86.7 85.3 Example 10 EC + EMC(1:3)Comparative 1,4-thioxane- 1 none — 1M LiPF₆/ 82.3 88.6 85.2 Example 111,1-dioxide EC + EMC(1:3) Example 18 1,4-thioxane- 3 vinylene 2 1MLiPF₆/ 87.4 91.2 85.3 1,1-dioxide carbonate EC + EMC(1:3) Comparative1,4-thioxane- 3 none — 1M LiPF₆/ 81.2 86.7 62.7 Example 12 1,1-dioxideEC + EMC(1:3) Example 19 1,4-thioxane- 0.5 vinylene 2 1M LiPF₆/ 87.592.2 88.3 1,1-dioxide carbonate EC + EMC(1:3) Comparative none —vinylene 2 1M LiPF₆/ 81.7 88.2 81.8 Example 13 carbonate EC + EMC(1:3)Example 20 1,4-thioxane- 1 vinylene 2 1M LiPF₆/ 85.3 92.2 87.61,1-dioxide carbonate EC + GBL(1:3)

Example 21

Using an electrolyte the same as in Example 15, a lithium secondarybattery was prepared, and continuous charge characteristic evaluationthe same as in Example 15 was conducted. Thereafter, the battery wasimmersed into an ethanol bath to measure buoyant force and the amount ofgas generation was calculated from the buoyant force. The amount of gasgeneration after 7 days of continuous charging was 0.54 ml.

Example 22

[Production of Negative Electrode]

With 95 parts by weight of natural graphite powder having a “d” valuefor a lattice plane (002 plane), as determined by X-ray diffraction, of0.336 nm, a crystallite size (Lc) of 652 nm, an ash content of 0.07% byweight, a median diameter as determined by the laserdiffraction/scattering method of 12 μm, a specific surface area asdetermined by BET method of 7.5 m²/g, and an “R” value (=I_(B)/I_(A)) of0.12 as determined by Raman spectroscopy with an argon ion laser light,and a half-band width of the peak appearing in the 1,570-1,620 cm⁻¹range of 19.9 cm⁻¹ was mixed 6 parts by weight of polyvinylidenefluoride, and N-methyl-2-pyrrolidone was added thereto to form a slurry.

This slurry was applied evenly onto one surface of a copper foil havinga thickness of 18 μm. After the coating was dried, the dried product waspressed so that the density of the negative active layer becomes 1.5g/cm³ to form a negative electrode.

[Production of Positive Electrode]

There are mixed 85% by weight of LiCoO₂, 6% by weight of carbon black,and 9% by weight of polyvinylidene fluoride (trade name “KF-1000”;manufactured by Kureha Chemical Co., Ltd.). N-Methyl-2-pyrrolidone wasadded thereto to prepare a slurry. This slurry was applied evenly onboth surfaces of an aluminum foil having a thickness of 20 μm. After thecoating was dried, the dried product was pressed so that the density ofthe positive active layer becomes 3.0 g/cm³ to form a positiveelectrode.

[Production of Lithium Secondary Battery]

The above positive electrode, negative electrode, and a separator madeof polyethylene were laminated in the order of the negative electrode,the separator, the positive electrode, the separator, and the negativeelectrode to prepare a cell element. The cell element was inserted intoa bag made of a laminate film obtained by covering both surfaces of analuminum (thickness 40 μm) with resin layers, while the terminals of thepositive electrode and the negative electrode was provided in anextended condition, and then the electrolyte to be mentioned below wasintroduced into the bag, which was vacuum-sealed to prepare a sheet-formlithium secondary battery.

[Capacity Evaluation]

In order to enhance the adhesiveness between the electrodes, while thelithium secondary battery was put between glass plates, the battery wascharged at a constant current corresponding to 0.2 C to 4.2V and thendischarged at a constant current of 0.2 C to 3V. This cycle was repeatedthree times to stabilize the battery. At the fourth cycle, the batterywas charged at a constant current of 0.5 C to 4.2V and then charged at aconstant voltage of 4.2V until the current value reached 0.05 C and thebattery was then discharged at 0.2 C to 3V to determined an initialdischarge capacity.

[Continuous Charge Characteristic Evaluation]

The battery after subjected to the capacity evaluation test was immersedinto an ethanol bath to measure a volume and was charged at a constantcurrent of 0.7 C at 60° C. and, when the voltage reached 4.25V, switchedto a constant-voltage charging, followed by one week of continuouscharging.

After cooling, the battery was immersed into an ethanol bath to measurea volume and the amount of gas was determined from the volume changebefore and after the continuous charging.

After the measurement of the amount of gas generation, the battery wasdischarged at a constant current of 0.2 C to 3V and a residual capacityafter the continuous charging test was measured to determine a residualcapacity after the continuous charging, the discharge capacity beforethe continuous charging test being taken as 100.

[High-Temperature Storage Characteristic Evaluation]

The battery after subjected to the capacity evaluation test was chargedat a constant current of 0.5 C to 4.2V and then charged at a constantvoltage of 4.2 V until the current value reached 0.05 C. Thereafter, thebattery was stored at 85° C. for 3 days. The battery was thoroughlycooled and then discharged at a constant current of 0.2 C to 3 V at 25°C. to determine a residual capacity after the storage test, thedischarge capacity before the storage being taken as 100.

[Cycle Characteristic Evaluation]

The battery after subjected to the capacity evaluation test wassubjected to a cycle test wherein the battery was charged at a constantcurrent of 0.5 C to 4.2 V at 25° C., then charged at a constant voltageof 4.2 V until the current value reached 0.05 C, and discharged at aconstant current of 1 C to 3 V. The discharge capacity after 200 cycleswas determined, the discharge capacity before the cycle test being takenas 100.

[Blending of Electrolyte]

Under a dry argon atmosphere, 2 parts by weight of vinylene carbonateand 1 part by weight of N,N-dimethylmethanesulfonamide were added to 97parts by weight of a mixture of ethylene carbonate and ethyl methylcarbonate (volume ratio 3:7) and then thoroughly dried LiPF₆ wasdissolved therein so as to achieve a ratio of 1.0 mol/L, whereby anelectrolyte was prepared.

Using the resulting electrolyte, a lithium secondary battery wasprepared and continuous charge characteristics, high-temperature storagecharacteristics, and cycle characteristics were evaluated. The resultsof the evaluation of continuous charge characteristics andhigh-temperature storage characteristics are shown in Table 7. Theresults of the evaluation of cycle characteristics are shown in Table 8.

Referential Example 3

One part by weight of N,N-dimethylmethanesulfonamide was added to 99parts by weight of a mixture of ethylene carbonate and ethyl methylcarbonate (volume ratio 3:7) and then thoroughly dried LiPF₆ wasdissolved therein so as to achieve a ratio of 1.0 mol/L, whereby anelectrolyte was prepared.

Using the resulting electrolyte, a lithium secondary battery wasprepared in the same manner as in Example 22 and continuous chargecharacteristics, high-temperature storage characteristics, and cyclecharacteristics were evaluated. The results of the evaluation ofcontinuous charge characteristics and high-temperature storagecharacteristics are shown in Table 7. The results of the evaluation ofcycle characteristics are shown in Table 8.

Comparative Example 14

Using an electrolyte obtained by dissolving thoroughly dried LiPF₆ intoa mixture of ethylene carbonate and ethyl methyl carbonate (volume ratio3:7) so as to achieve a ratio of 1.0 mol/L, a lithium secondary batterywas prepared in the same manner as in Example 22, and then continuouscharge characteristics, high-temperature storage characteristics, andcycle characteristics were evaluated. The results of the evaluation ofcontinuous charge characteristics and high-temperature storagecharacteristics are shown in Table 7. The results of the evaluation ofcycle characteristics are shown in Table 8.

Comparative Example 15

One part by weight of 1,1-sulfonyldiimidazole was added to 99 parts byweight of a mixture of ethylene carbonate and ethyl methyl carbonate(volume ratio 3:7) and then thoroughly dried LiPF₆ was dissolved thereinso as to achieve a ratio of 1.0 mol/L, whereby an electrolyte wasprepared.

Using the electrolyte, a lithium secondary battery was prepared in thesame manner as in Example 22, and continuous charge characteristics andhigh-temperature storage characteristics were evaluated. The results areshown in Table 7.

Comparative Example 16

Two parts by weight of vinylene carbonate was added to 98 parts byweight of a mixture of ethylene carbonate and ethyl methyl carbonate(volume ratio 3:7) and then thoroughly dried LiPF₆ was dissolved thereinso as to achieve a ratio of 1.0 mol/L, whereby an electrolyte wasprepared.

Using the electrolyte, a lithium secondary battery was prepared in thesame manner as in Example 22 and continuous charge characteristics,high-temperature storage characteristics, and cycle characteristics wereevaluated. The results of the evaluation of continuous chargecharacteristics and high-temperature storage characteristics are shownin Table 7. The results of the evaluation of cycle characteristics areshown in Table 8.

Comparative Example 17

Two parts by weight of vinylene carbonate and 1 part by weight of1,1-sulfonyldiimidazole were added to 97 parts by weight of a mixture ofethylene carbonate and ethyl methyl carbonate (volume ratio 3:7) andthen thoroughly dried LiPF₆ was dissolved therein so as to achieve aratio of 1.0 mol/L, whereby an electrolyte was prepared.

Using the electrolyte, a lithium secondary battery was prepared in thesame manner as in Example 22, and continuous charge characteristics andhigh-temperature storage characteristics were evaluated. The results areshown in Table 7.

Comparative Example 18

Two parts by weight of vinylene carbonate and 1 part by weight of1-p-tolylsulfonylpyrrole were added to 97 parts by weight of a mixtureof ethylene carbonate and ethyl methyl carbonate (volume ratio 3:7) andthen thoroughly dried LiPF₆ was dissolved therein so as to achieve aratio of 1.0 mol/L, whereby an electrolyte was prepared.

Using the electrolyte, a lithium secondary battery was prepared in thesame manner as in Example 22, and continuous charge characteristics andhigh-temperature storage characteristics were evaluated. The results areshown in Table 7.

Example 23

Two parts by weight of vinylene carbonate and 0.5 part by weight ofN,N-dimethylmethanesulfonamide were added to 97.5 parts by weight of amixture of ethylene carbonate and ethyl methyl carbonate (volume ratio3:7) and then thoroughly dried LiPF₆ was dissolved therein so as toachieve a ratio of 1.0 mol/L, whereby an electrolyte was prepared.

Using the electrolyte, a lithium secondary battery was prepared in thesame manner as in Example 22, and continuous charge characteristics andhigh-temperature storage characteristics were evaluated. The results areshown in Table 7.

Example 24

Two parts by weight of vinylene carbonate and 0.5 part by weight ofN,N-dimethylethanesulfonamide were added to 97.5 parts by weight of amixture of ethylene carbonate and ethyl methyl carbonate (volume ratio3:7) and then thoroughly dried LiPF₆ was dissolved therein so as toachieve a ratio of 1.0 mol/L, whereby an electrolyte was prepared.

Using the electrolyte, a lithium secondary battery was prepared in thesame manner as in Example 22, and continuous charge characteristics andhigh-temperature storage characteristics were evaluated. The results areshown in Table 7.

Example 25

Two parts by weight of vinylene carbonate and 0.5 part by weight ofN,N-dibutylbenzenesulfonamide were added to 97.5 parts by weight of amixture of ethylene carbonate and ethyl methyl carbonate (volume ratio3:7) and then thoroughly dried LiPF₆ was dissolved therein so as toachieve a ratio of 1.0 mol/L, whereby an electrolyte was prepared.

Using the electrolyte, a lithium secondary battery was prepared in thesame manner as in Example 22, and continuous charge characteristics andhigh-temperature storage characteristics were evaluated. The results areshown in Table 7. TABLE 7 Additive Unsaturated carbonate ResidualContent Content capacity after part by part by Amount of gas continuousResidual capacity Compound weight Compound weight generation (ml)charging (%) after storage (%) Example 22 N,N-dimethylmethane- 1vinylene 2 0.43 94 80 sulfonamide carbonate ReferentialN,N-dimethylmethane- 1 none — 0.34 90 73 Example 3 sulfonamideComparative — — none — 0.41 88 69 Example 14 Comparative 1,1′-sulfonyl-1 none — 0.25 79 65 Example 15 diimidazole Comparative — — vinylene 20.67 84 75 Example 16 carbonate Comparative 1,1′-sulfonyl- 1 vinylene 20.53 85 72 Example 17 diimidazole carbonate Comparative1-p-tolylsulfonyl- 1 vinylene 2 0.56 46 67 Example 18 pyrrole carbonateExample 23 N,N-dimethylmethane- 0.5 vinylene 2 0.39 96 81 sulfonamidecarbonate Example 24 N,N-dimethylethane- 0.5 vinylene 2 0.44 92 80sulfonamide carbonate Example 25 N,N-dibutylbenzene- 0.5 vinylene 2 0.5098 81 Sulfonamide carbonate

TABLE 8 Discharge capacity after 200 cycles (%) Example 22 90Referential Example 3 82 Comparative Example 14 80 Comparative Example16 90

Example 26

Two parts by weight of vinylene carbonate and 3 part by weight offluorobenzene were added to 95 parts by weight of a mixture of ethylenecarbonate and ethyl methyl carbonate (volume ratio 3:7) and thenthoroughly dried LiPF₆ was dissolved therein so as to achieve a ratio of1.0 mol/L, whereby an electrolyte was prepared.

Using the electrolyte, a lithium secondary battery was prepared in thesame manner as in Example 22.

Comparative Example 19

Thoroughly dried LiPF₆ was dissolved into a mixture of ethylenecarbonate and ethyl methyl carbonate (volume ratio 3:7) so as to achievea ratio of 1.0 mol/L, whereby an electrolyte was prepared. A sheet-formbattery was prepared in the same manner as in Example 26 with theexception that the electrolyte was used.

Comparative Example 20

Two parts by weight of vinylene carbonate was added to 98 parts byweight of a mixture of ethylene carbonate and ethyl methyl carbonate(volume ratio 3:7), and then thoroughly dried LiPF₆ was dissolvedtherein so as to achieve a ratio of 1.0 mol/L, whereby an electrolytewas prepared. A sheet-form battery was prepared in the same manner as inExample 26 with the exception that the electrolyte was used.

Comparative Example 21

Two parts by weight of vinylene carbonate and 5 parts by weight oftrimethyl phosphate were added to 93 parts by weight of a mixture ofethylene carbonate and ethyl methyl carbonate (volume ratio 3:7), andthen thoroughly dried LiPF₆ was dissolved therein so as to achieve aratio of 1.0 mol/L, whereby an electrolyte was prepared. A sheet-formbattery was prepared in the same manner as in Example 26 with theexception that the electrolyte was used.

Example 27

Two parts by weight of vinylene carbonate and 3 parts by weight offluorobenzene were added to 95 parts by weight of a mixture of ethylenecarbonate and ethyl methyl carbonate (volume ratio 3:7), and thenthoroughly dried LiPF₆ was dissolved therein so as to achieve a ratio of1.0 mol/L and LiN(CF₃SO₂)₂ was dissolved therein so as to achieve aratio of 0.1 mol/L, whereby an electrolyte was prepared. A sheet-formbattery was prepared in the same manner as in Example 26 with theexception that the electrolyte was used.

Example 28

Two parts by weight of vinylene carbonate, 3 parts by weight offluorobenzene, and 1 part by weight of cyclohexylbenzene were added to94 parts by weight of a mixture of ethylene carbonate and ethyl methylcarbonate (volume ratio 3:7), and then thoroughly dried LiPF₆ wasdissolved therein so as to achieve a ratio of 1.0 mol/L, whereby anelectrolyte was prepared. A sheet-form battery was prepared in the samemanner as in Example 26 with the exception that the electrolyte wasused.

Comparative Example 22

Two parts by weight of vinylene carbonate and 1 part by weight ofcyclohexylbenzene were added to 97 parts by weight of a mixture ofethylene carbonate and ethyl methyl carbonate (volume ratio 3:7), andthen thoroughly dried LiPF₆ was dissolved therein so as to achieve aratio of 1.0 mol/L, whereby an electrolyte was prepared. A sheet-formbattery was prepared in the same manner as in Example 26 with theexception that the electrolyte was used.

Example 29

In Example 26, the product pressed to have a density of the negativeelectrode layer of 1.5 g/cm³ by a pressing machine was punched out toobtain a disk having a diameter of 12.5 mm, which was used as a negativeelectrode. As for a positive electrode, the positive activematerial-containing slurry prepared in Example 26 was evenly appliedonto one surface of an aluminum foil having a thickness of 20 μm as acurrent collector for the positive electrode and dried, and then pressedby a pressing machine so that the density of the positive electrodelayer became 3.0 g/cm³, followed by punching out the coated one toobtain a disk having a diameter of 12.5 mm, which was used as thepositive electrode.

Under a dry argon atmosphere, 1 part by weight of vinylene carbonate, 1part by weight of vinylethylene carbonate and 7 parts by weight offluorobenzene were added to 91 parts by weight of a mixture of ethylenecarbonate and γ-butyrolactone (volume ratio 3:7), and then thoroughlydried LiBF₄ was dissolved therein so as to achieve a ratio of 1.5 mol/L,whereby an electrolyte was prepared.

The positive electrode was placed in a stainless-steel can serving alsoas a positive-electrode conductor. Thereon was placed the negativeelectrode impregnated with the electrolyte via a polyethylene separatorimpregnated with the electrolyte. This can was caulked and sealed with aseal plate serving also as a negative-electrode conductor via a gasketfor insulation to prepare a coin-shaped battery. Therein, theimpregnation of battery members with the electrolyte was conducted byimmersing each member in the electrolyte for 2 minutes.

Comparative Example 23

One part by weight of vinylene carbonate and 1 part by weight ofvinylethylene carbonate were added to 98 parts by weight of a mixture ofethylene carbonate and γ-butyrolactone (volume ratio 3:7), and thenLiBF₄ was dissolved therein so as to achieve a ratio of 1.5 mol/L,whereby an electrolyte was prepared. A coin-shaped battery was preparedin the same manner as in Example 29 with the exception that theelectrolyte was used.

Comparative Example 24

One part by weight of vinylene carbonate and 1 part by weight ofvinylethylene carbonate were added to 98 parts by weight of a mixture ofethylene carbonate, γ-butyrolactone, and ethyl methyl carbonate (volumeratio 3:5:2), and then LiBF₄ was dissolved therein so as to achieve aratio of 1.5 mol/L, whereby an electrolyte was prepared. A coin-shapedbattery was prepared in the same manner as in Example 29 with theexception that the electrolyte was used.

[Battery Evaluation]

In order to enhance the adhesiveness between the electrodes, while thelithium secondary battery was put between glass plates, each of thebatteries of Examples 26 to 28 and Comparative Examples 19 to 22 wascharged at a constant current corresponding to 0.2 C to a final voltageof 4.2 V and then discharged to a final voltage of 3V. This cycle wasrepeated three times to stabilize the battery. At the fourth cycle, thebattery was subjected to 4.2 V-constant-current constant-voltagecharging (CCCV charge) (0.05 C cut) wherein it was charged at a currentcorresponding to 0.5 C to a final voltage of 4.2 V and then chargeduntil the current value reached a current value corresponding to 0.05 C.

Thereafter, the battery was discharged at a constant currentcorresponding to 0.2 C to 3 V. Further, continuous charging of 4.2V-CCCV at 60° C. was conducted for 2 weeks.

Before and after the continuous charge test at 4.2 V-CCCCV at 60° C.,the sheet-form battery was immersed into an ethanol bath and the amountof gas generation was determined from the change of the buoyant force.

Moreover, with regard to the batteries of Examples 26 and 27 andComparative Examples 19 to 21, after the buoyant force measurement, eachof the batteries was discharged at a constant current of 0.2 C to afinal discharge voltage of 3 V at 25° C. to measure a residual capacityafter the continuous charge test.

Then, after charging at 4.2 V-CCCCV (0.05 C cut) and discharging at aconstant current of 0.2 C to a final discharge voltage of 3 V, thebattery was charged under the same CCCV conditions and discharged at acurrent value corresponding to 1.5 C to 3 V to measure high-loaddischarge characteristics. Therein, 1 C means a current value at whichthe battery can be fully charged over a period of 1 hour and 1.5 C meansthe current value that is 1.5 times as much as 1 C.

The amount of gas generation, the residual capacity after the continuouscharging when the discharge capacity before the continuous charging istaken as 100, and the capacity at the high-load discharging are shown inTable 9. TABLE 9 High-load Amount of gas Residual discharge generation(ml) capacity (%) capacity (%) Example 26 0.38 93.4 80.4 Comparative0.53 86.3 79.1 Example 19 Comparative 0.92 91.5 75.8 Example 20Comparative 0.61 91.5 23.9 Example 21 Example 27 0.32 93.7 81.7 Example28 1.18 — — Comparative 1.57 — — Example 22

Example 22

Each of the batteries of Example 29 and Comparative Examples 23 and 24was charged at a constant current of 0.5 mA to a final voltage of 4.2 Vand then discharged to a final voltage of 3V. This cycle was repeatedthree times to stabilize the battery. Then, a cycle test was conducted,wherein the battery was subjected to 4.2 V-CCCV charge (0.05 C cut) thatincludes charge at a current corresponding to 0.7 C to a final voltageof 4.2 V and subsequent charge until the current value reached a currentvalue corresponding to 0.05 C, and then subjected to discharge at aconstant current corresponding to 1 C to a final discharge voltage of 3V. The capacity at the 50th cycle is shown in Table 10, the dischargecapacity at the fourth cycle being taken as 100. TABLE 10 Capacity after50 cycles (%) Example 29 91.2 Comparative Example 23 impossible tocharge Comparative Example 24 87.3

Moreover, when the amount of gases (total amount of methane, ethane,ethylene, CO, and CO₂ generated) inside the battery after 50 cycles wasmeasured by gas chromatography, the amount of gases in the battery ofExample 29 was found to be 77, the amount of gases in the battery ofComparative Example 24 being taken as 100.

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made therein withoutdeparting from the spirit and scope thereof.

This application is based on a Japanese patent application filed on Mar.8, 2002 (Patent Application No. 2002-063545), a Japanese patentapplication filed on Mar. 8, 2002 (Patent Application No. 2002-063547),a Japanese patent application filed on Aug. 21, 2002 (Patent ApplicationNo. 2002-240382), a Japanese patent application filed on Oct. 10, 2002(Patent Application No. 2002-297359), a Japanese patent applicationfiled on Jan. 9, 2003 (Patent Application No. 2003-003268), and aJapanese patent application filed on Feb. 6, 2003 (Patent ApplicationNo. 2003-029983), the entire contents thereof being hereby incorporatedby reference.

INDUSTRIAL APPLICABILITY

According to the invention, it is possible to prepare a battery of highcapacity that is excellent in storage characteristics, loadcharacteristics, and, in case of a secondary battery, cyclecharacteristics and continuous charge characteristics and that reducesgas generation, and thus size reduction and enhanced performance of anonaqueous electrolyte battery can be achieved.

1. A nonaqueous electrolyte which comprises a nonaqueous organic solventand a lithium salt dissolved therein, wherein the nonaqueous organicsolvent comprises at least one compound selected from the groupconsisting of acid anhydrides and carbonic esters having an unsaturatedbond, and at least one compound selected from the group consisting of[A] and [B]; [A]: sulfonic compounds represented by any one of formulae(1), (3), (4) and (5):

wherein L¹ represents a Z¹-valent connecting group composed of carbonatom(s) and hydrogen atoms, R¹ represents a hydrocarbon group, and Z¹ isan integer of 3 or more;

wherein each of R³ to R⁷ independently represents a hydrogen atom or ahydrocarbon group having 1 to 8 carbon atoms, R⁸ represents ahydrocarbon group having 1 to 8 carbon atoms, and n³ represents aninteger of 0 to 4;

wherein each of R⁹ to R¹² independently represents a hydrogen atom or ahydrocarbon group having 1 to 8 carbon atoms, or R⁹ and R¹⁰, R¹¹ and R¹²each may be combined with each other to form a ring and R¹⁰ and R¹¹ maybe also combined with each other; and

wherein each of R¹³ to R¹⁵ independently represents an alkyl grouphaving 1 to 12 carbon atoms which may be substituted with fluorineatom(s), an alkenyl group having 2 to 12 carbon atoms which may besubstituted with fluorine atom(s), an aryl group having 6 to 12 carbonatoms which may be substituted with fluorine atom(s), or an aralkylgroup having 7 to 12 carbon atoms which may be substituted with fluorineatom(s), or R¹⁴ and R¹⁵ may be combined with each other to form anitrogen-containing aliphatic ring and R¹³ and R¹⁴ may be combined witheach other to form a cyclic structure; [B]: fluorine-containing aromaticcompounds having 9 carbon atoms or less.
 2. The nonaqueous electrolyteaccording to claim 1, wherein the total content of the compound selectedfrom the group consisting of [A] and [B] is 0.01 to 15% by weight basedon the nonaqueous electrolyte.
 3. The nonaqueous electrolyte accordingto claim 1, wherein the total content of the compound selected from thegroup consisting of [A] and [B] is 0.01 to 10% by weight based on thenonaqueous electrolyte.
 4. The nonaqueous electrolyte according to claim1, wherein the total content of the compound selected from the groupconsisting of [A] and [B] is 0.01 to 5% by weight based on thenonaqueous electrolyte.
 5. The nonaqueous electrolyte according to claim1, which comprises a cyclic carbonic ester having an unsaturated bond.6. The nonaqueous electrolyte according to claim 1, which comprises acyclic carbonic ester having an unsaturated bond in an amount of 0.01 to10% by weight.
 7. The nonaqueous electrolyte according to claim 1, whichcomprises a cyclic carbonic ester having an unsaturated bond in anamount of 0.01 to 8% by weight.
 8. A lithium secondary battery employingthe nonaqueous electrolyte according to claim
 1. 9. A nonaqueouselectrolyte which comprises a nonaqueous organic solvent and a lithiumsalt dissolved therein, wherein the nonaqueous organic solvent comprisesa sulfonic compound represented by formula (1):

wherein L¹ represents a Z¹-valent connecting group composed of carbonatom(s) and hydrogen atoms, R¹ represents a hydrocarbon group, and Z¹ isan integer of 3 or more.
 10. The nonaqueous electrolyte according toclaim 9, wherein the total content of the sulfonic compound representedby formula (1) is 0.01 to 15% by weight based on the nonaqueouselectrolyte.
 11. The nonaqueous electrolyte according to claim 9,wherein the total content of the sulfonic compound represented byformula (1) is 0.01 to 10% by weight based on the nonaqueouselectrolyte.
 12. The nonaqueous electrolyte according to claim 9,wherein the total content of the sulfonic compound represented byformula (1) is 0.01 to 5% by weight based on the nonaqueous electrolyte.13. A lithium secondary battery employing the nonaqueous electrolyteaccording to claim
 9. 14. A nonaqueous electrolyte which comprises anonaqueous organic solvent and a lithium salt dissolved therein, whereinthe nonaqueous organic solvent comprises a sulfonic compound representedby formula (2):

wherein L² represents a Z²-valent connecting group composed of carbonatom(s) and hydrogen atoms, R² represents a fluorinated aliphaticsaturated hydrocarbon group, n² is an integer of 1 or more, and Z² is aninteger of 2 or more.
 15. The nonaqueous electrolyte according to claim14, wherein the total content of the sulfonic compound represented byformula (2) is 0.01 to 15% by weight based on the nonaqueouselectrolyte.
 16. The nonaqueous electrolyte according to claim 14,wherein the total content of the sulfonic compound represented byformula (2) is 0.01 to 10% by weight based on the nonaqueouselectrolyte.
 17. The nonaqueous electrolyte according to claim 14,wherein the total content of the sulfonic compound represented byformula (2) is 0.01 to 5% by weight based on the nonaqueous electrolyte.18. A lithium secondary battery employing the nonaqueous electrolyteaccording to claim
 14. 19. A nonaqueous electrolyte which comprises anonaqueous organic solvent and a lithium salt dissolved therein, whereinthe nonaqueous organic solvent comprises a sulfonic compound representedby formula (5):

wherein each of R¹³ to R¹⁵ independently represents an alkyl grouphaving 1 to 12 carbon atoms which may be substituted with fluorineatom(s), an alkenyl group having 2 to 12 carbon atoms which may besubstituted with fluorine atom(s), an aryl group having 6 to 12 carbonatoms which may be substituted with fluorine atom(s), or an aralkylgroup having 7 to 12 carbon atoms which may be substituted with fluorineatom(s), or R¹⁴ and R¹⁵ may be combined with each other to form anitrogen-containing aliphatic ring and R¹³ and R¹⁴ may be combined witheach other to form a cyclic structure.
 20. The nonaqueous electrolyteaccording to claim 19, wherein the total content of the sulfoniccompound represented by formula (5) is 0.01 to 15% by weight based onthe nonaqueous electrolyte.
 21. The nonaqueous electrolyte according toclaim 19, wherein the total content of the sulfonic compound representedby formula (5) is 0.01 to 10% by weight based on the nonaqueouselectrolyte.
 22. The nonaqueous electrolyte according to claim 19,wherein the total content of the sulfonic compound represented byformula (5) is 0.01 to 5% by weight based on the nonaqueous electrolyte.23. A lithium secondary battery employing the nonaqueous electrolyteaccording to claim 19.